Below is the best brief description of the beginning of Christianity that you will find. This is what the apostles' churches believed and practiced directly from early Christian literature.
Many people believe that we either know very little about early Christianity, or they think it all Roman Catholic. Not true! The early Christian literature gives us a clear picture, at least in general, of what the beginning of Christianity was like.
The following is what the apostles' churches said about themselves.
3rd century catacombs painting of Jesus as the Good Shepherd
Core Essential Beliefs at the Beginning of Christianity
From A.D. 185
The Church, though dispersed through our the whole world, even to the ends of the earth, has received from the apostles and their disciples this faith:
In one God, the Father Almighty, Maker of heaven, earth, the sea, and everything in them;
And in one Christ Jesus, the Son of God, who became incarnate for our salvation;
And in the Holy Spirit,
The Incarnation, Death, and Resurrection of Christ
Who proclaimed through the prophets the dispensations and the advents, the birth from a virgin, the suffering, the resurrection from the dead, and the ascension into heaven in the flesh of the beloved Christ Jesus, our Lord;
The Return of Christ
[The Spirit] also [proclaimed] his manifestation from heaven in the glory of the Father to gather all things in one and to raise up anew all flesh of the whole human race, in order that to Christ Jesus—our Lord, God, Saviour, King—according to the will of the invisible Father, every knee should bow—of things in heaven, things in earth, and things under the earth—and that every tongue should confess to him;
That he should execute just judgment towards all;
That he may send spiritual wickednesses and the angels who transgressed and became apostates—together with the ungodly, unrighteous, wicked, and profane among men—into everlasting fire;
That he may, in the exercise of his grace, confer immortality on the righteous, holy, and those who have kept his commandments and have persevered in his love—some from the beginning and others from their repentance—and may surround them with everlasting glory. (Irenaeus, Against Heresies, I:10:1)
Irenaeus learned his doctrine sitting at the feet of Polycarp, bishop of Smyrna, one of the two churches that received only praise from our Lord in his letters of Revelation 2 and 3. He went from Smyrna in modern Turkey all the way across southern Europe to form churches among the Celtic Gauls of modern France. Everywhere he went, he said, even among the Barbarians, the churches of God had clung to the traditions [that's not a cuss word—1 Cor. 11:2; 2 Thess. 2:15] they had received from the apostles:
[The Church] believes these points as if she had but one soul and one and the same heart. She proclaims them, teaches them, and hands them down with perfect harmony, as if she possessed only one mouth. For although the languages of the world are dissimilar, yet the meaning of the tradition is one and the same.
For the Churches which have been planted in Germany do not believe or hand down anything different. Nor do those in Spain, nor those in Gaul, nor those in the East, nor those in Egypt, nor those in Libya, nor those which have been established in the central regions of the world. (ibid., I:10:2)
And just as he tells us what all Christians believe, he also lists things that not essential at the beginning of Christianity. Instead, the gifted among them were granted to explore these subjects for the benefit of others.
It does not follow that because men are endowed with greater and lesser degrees of intelligence, they should therefore change the subject matter [of the faith] itself ...
But ... one may bring out the meaning of those things which have been spoken in parables and accommodate them to the general scheme of the faith. He may explain the operation and dispensation of God connected with human salvation.
He may show that God showed patience regarding the apostasy of the angels who transgressed and also concerning the disobedience of men. ...
He may show why it was that more covenants than one were given to mankind and teach the special character of each of these covenants. He may search out why God hath included everyone in unbelief so that he may have mercy upon all. He may gratefully describe for what purpose the Word of God became flesh and suffered and explain why the coming of the Son of God took place in these last times—that is, in the end rather than in the beginning. He may unfold what is contained in the Scriptures concerning the end and things to come. ...
In reference to these points, and others like them, the apostle exclaims, "Oh, the depth of the riches of both the wisdom and knowledge of God! How unsearchable are his judgments, and his ways past finding out!" (ibid., I:10:3)
Gatherings/Meetings/Services at the Beginning of Christianity
From A.D. 150
The wealthy among us help the needy, and we always keep together. For all things with which we are supplied, we bless the Maker of all through his Son Jesus Christ and through the Holy Spirit.
On the day called Sunday, all who live in cities or in the country gather together in one place, and the memoirs of the apostles or the writings of the prophets are read, as long as time permits. Then, when the reader has ceased, the president [I think this means whichever brother is presiding, but no one knows for sure] verbally instructs and exhorts to the imitation of these good things.
Then we all rise together and pray, and … when our prayer is ended, bread and wine and water are brought, and the president in like manner offers prayers and thanksgivings according to his ability, and the people assent, saying Amen. There is a distribution to each and a participation of that over which thanks have been given, and to those who are absent a portion is sent by the deacons.
They who are well to do and willing give what each thinks fit, and what is collected is deposited with the president. He helps the orphans, widows, and those who, through sickness or any other cause, are in need. [He helps] those who are in bonds and the strangers sojourning among us. In a word [he] takes care of all who are in need.
But Sunday is the day on which we all hold our common assembly, because it is the first day on which God, having made a change in darkness and matter, made the world. On the same day Jesus Christ our Savior rose from the dead. For he was crucified on the day before that of Saturn [Saturday], and on the day after that of Saturn, which is the day of the Sun, he appeared to his apostles and disciples and taught them these things. (Justin Martyr, First Apology ch. 67)
From A.D. 210
We meet together as an assembly and congregation so that, offering up prayer to God as with united force, we may wrestle with him in our supplications. This violence God delights in. We pray, too, for the emperors, their ministers and all in authority; for the welfare of the world, for the prevalence of peace, and for the delay of the final consummation.
We assemble to read our sacred writings, if any peculiarity of the times makes either forewarning or reminiscence needful. Either way, with the sacred words we nourish our faith, we animate our hope, and we make our confidence more stedfast.
By nothing less than indoctrination in God's precepts we confirm good habits. In the same place also exhortations are made; rebukes and sacred censures are administered.
With great gravity the work of judging is carried on among us, as is fitting for those who feel assured that they are in the sight of God. And you have the most notable example of judgment to come when any one has sinned so grievously as to require his severance from us in prayer, in the congregation and in all sacred intercourse.
The tried men of our elders preside over us, obtaining that honor not by purchase, but by established character.
There is no buying and selling of any sort in the things of God. Though we have our treasure chest, it is not made up of purchase money, as of a religion that has its price. On the monthly day, if he likes, each puts in a small donation; but only if it be his pleasure and only if he be able. There is no compulsion; all is voluntary. These gifts are, as it were, piety's deposit fund.
They are not taken from there and spent on feasts, drinking bouts, and eating houses, but to support and bury poor people, to supply the needs of boys and girls destitute of means and parents; of old persons confined now to the house; such, too, as have suffered shipwreck; and if there happen to be any in the mines, banished to the islands, or shut up in the prisons for nothing but their faithfulness to the cause of God's Church. These become the nurslings of their confession. (Tertullian, Apology, ch. 39)
Fellowship at the Beginning of Christianity
From A.D. 100
You shall seek out the faces of the saints every day so that you may rest upon their words. You shall not long for division, but shall bring those who contend to peace …You shall not turn away from him that is in need, but you shall share all things with your brother and shall not say that they are your own. For if you share what is immortal, how much more things which are temporary? (The Teaching of the Twelve Apostles, ch. 4, A.D. 80 - 120)
From A.D. 150
Since our persuasion by the Word, we stand aloof from [the demons involved in idolatry] and follow the only unbegotten God through His Son.
We who formerly delighted in fornication now embrace chastity alone. We who formerly used magical arts dedicate ourselves to the good and unbegotten God. We who valued above all things the acquisition of wealth and possessions now bring what we have into a common stock and share with every one in need. We who hated and destroyed one another and would not live with men of a different tribe because of their different customs now, since the coming of Christ, share the same fire with them.
We pray for our enemies and attempt to persuade those who hate us unjustly to live according to the good precepts of Christ. This is so that they may become partakers with us of the same joyful hope of a reward from God, the Ruler of all. (Justin Martyr, First Apology, ch. 14)
From A.D. 210
It is mainly the deeds of a love so noble that lead many to label us. "See," they say, "How they love one another!" For themselves are animated by mutual hatred. "How they are ready even to die for one another!" For they themselves will sooner put to death.
They are angry with us, too, because we call each other brethren. There is no other reason for this, I think, than because among them names of consanguinity are given in mere pretence of affection. ...
How much more fittingly they are called and counted brothers who have been led to the knowledge of God as their common Father? Who have drunk in one Spirit of holiness? Who from the same womb of a common ignorance have agonized into the same light of truth?
But perhaps the very reason we are regarded as having less right to be considered true brothers is that no tragedy causes dissension in our brotherhood. Or maybe it is that the family possessions, which generally destroy brotherhood among you, create fraternal bonds among us. One in mind and soul, we do not hesitate to share our earthly goods with one another. All things are common among us but our wives. (Tertullian, Apology, ch. 39, c. A.D. 210)
Baptism at the Beginning of Christianity
From A.D. 100
Concerning baptism, baptize in this way: Having first said all these things [i.e., the commands contained in the Way of Life and Death contained in first 6 chapters of the Didache], baptize into the name of the Father and of the Son and of the Holy Spirit in running water. But if you have no running water, baptize into other water. If you cannot baptize in cold, then in warm. But if you have neither, pour water three times upon the head in the name of the Father, Son, and Holy Spirit. However, before baptism, let the baptizer fast, and the baptized, and whoever else can. Either way, you shall order the baptized to fast one or two days before. (The Teaching of the Twelve Apostles, ch. 7)
From A.D. 150
I will also tell you how we dedicated ourselves to God once we had been made new through Christ. … As many as are persuaded and believe that what we teach and say is true—and who determine to live accordingly—are instructed to pray and entreat God with fasting for the remission of their sins of the past. We pray and fast with them.
Then they are brought by us where there is water, and they are regenerated in the same manner in which we ourselves were regenerated. For in the name of God, the Father and Lord of the universe, of our Savior Jesus Christ, and of the Holy Spirit, they receive the washing with water. For Christ also said, "Unless you are born again, you shall not enter the kingdom of heaven" [John 3:3]. …
How those who have sinned and repent shall escape their sins is declared by Isaiah the prophet, as I said earlier. He speaks in this way: "'Wash yourselves; make yourselves clean. Put away the evil of your doings from your souls. Learn to do good. Judge the fatherless, and plead for the widow. Then come, let us reason together,' says the Lord, 'and though your sins are as scarlet, I will make them white like wool … '"
We have learned from the apostles the following reason for all this: at our birth we were born without our knowledge or choice—by our parents coming together—and we were brought up in bad habits and wicked training.
So that we would not remain the children of necessity and ignorance but become the children of choice and knowledge, and so that we may obtain in the water the forgiveness of sins formerly committed, there is pronounced over the the person who chooses to be born again and who has repented of their sins, the name of God, the Father and Lord of the universe.
He who leads the person that is to be washed to the laver calls God by this name alone … And this washing is called illumination because those who learn these things are illuminated in their understanding.
The one who is illuminated is also washed in the name of Jesus Christ, who was crucified under Pontius Pilate, and in the name of the Holy Spirit, who through the prophets foretold all things about Jesus. (First Apology 61)
Ordination of Leaders at the Beginning of Christianity
From A.D. 210
The tried men of our elders preside over us, obtaining that honor not by purchase, but by established character. There is no buying and selling of any sort in the things of God. (Tertullian, Apology, ch. 39, c. A.D. 210)
From A.D. 250
Cyprian's Leadership Quotes
Be careful to note the difference between the requirements for ordaining a bishop and the requirements for ordaining an elder in Cyprian's leadership quotes.
Otherwise, Cyprian will seem to be contradicting himself.
Only the appointment of a bishop required the attendance and approval of surrounding bishops. Elders could be approved by the congregation alone.
Nor let the people flatter themselves that they can be free from the contagion of sin, while communicating with an elder who is a sinner, and yielding their consent to the unjust and unlawful episcopacy of their overseer …
On which account a people obedient to the Lord's precepts, and fearing God, ought to separate themselves from a sinful prelate, and not to associate themselves with the sacrifices of a sacrilegious priest, especially since they themselves have the power either of choosing worthy elders, or of rejecting unworthy ones. ("To the Clergy and People Abiding in Spain," par. 3, from the Epistles of Cyprian 67, as numbered in The Ante-Nicene Fathers, vol. V)
God commands an elder to be appointed in the presence of all the assembly; that is, He instructs and shows that the ordination of elders ought not to be solemnized except with the knowledge of the people standing near, that in the presence of the people either the crimes of the wicked may be disclosed, or the merits of the good may be declared, and the ordination, which shall have been examined by the vote and judgment of all, may be just and legitimate. ("To the Clergy and People Abiding in Spain," par. 4, from the Epistles of Cyprian 67, as numbered in The Ante-Nicene Fathers, vol. V)
Cyprian of Carthage, Martyred A.D. 258
For which reason you must diligently observe and keep the practice delivered from divine tradition and apostolic observance, which is also maintained among us, and almost throughout all the provinces; that for the proper celebration of ordinations all the neighbouring bishops of the same province should assemble with that people for which a prelate is ordained. And the bishop should be chosen in the presence of the people, who have most fully known the life of each one, and have looked into the doings of each one as respects his habitual conduct. ("To the Clergy and People Abiding in Spain," par. 5, from the Epistles of Cyprian 67, as numbered in The Ante-Nicene Fathers, vol. V)
As there are many other and grave crimes in which Basilides and Martialis are held to be implicated; such persons attempt to claim for themselves the episcopate [office of bishop] in vain; since it is evident that men of that kind may neither rule over the Church of Christ, nor ought to offer sacrifices to God … men of this sort might indeed be admitted to repentance, but were prohibited from the ordination of the clergy, and from the priestly honor. ("To the Clergy and People Abiding in Spain," par. 5, from the Epistles of Cyprian 67, as numbered in The Ante-Nicene Fathers, vol. V)