First Century Christianity

The Didache or The Lord's Teaching Through the Twelve Apostles to the Nations was probably written toward the end of the First Century (in other words, before a "New Testament" existed) and provides the earliest known summary of the fundamentals of Christianity:

There are two ways, one of life and one of death; but a great difference between the two ways. The way of life, then, is this: First, you shall love God who made you; second, your neighbor as yourself; and all things whatsoever you would should not occur to you, do not also do to another. And of these sayings the teaching is this: Bless those who curse you, and pray for your enemies, and fast for those who persecute you. For what reward is there, if you love those who love you? Do not also the Gentiles do the same? But love those who hate you, and you shall not have an enemy. Abstain from fleshly and worldly lusts. If someone gives you a blow upon your right cheek, turn to him the other also, and you shall be perfect. If someone impresses you for one mile, go with him two. If someone takes away your cloak, give him also your coat. If someone takes from you what is yours, ask it not back, for indeed you are not able. Give to every one that asks you, and ask it not back; for the Father wills that to all should be given of our own blessings (free gifts). Happy is he that gives according to the commandment; for he is guiltless. Woe to him that receives; for if one having need receives, he is guiltless; but he that receives not having need, shall pay the penalty, why he received and for what, and, coming into straits (confinement), he shall be examined concerning the things which he has done, and he shall not escape thence until he pay back the last farthing. But also now concerning this, it has been said, Let your alms sweat in your hands, until you know to whom you should give.

**Several sections follow this one on sins/behaviors that are forbidden to Christians (e.g. murder, adultery, witchcraft, hate, anger, idolatry, blasphemy, etc.)********************************

And concerning baptism, baptize this way: Having first said all these things, baptize into the name of the Father, and of the Son, and of the Holy Spirit, in living water. But if you have not living water, baptize into other water; and if you can not in cold, in warm. But if you have not either, pour out water thrice upon the head into the name of Father and Son and Holy Spirit. But before the baptism let the baptizer fast, and the baptized, and whatever others can; but you shall order the baptized to fast one or two days before.

But let not your fasts be with the hypocrites; for they fast on the second and fifth day of the week; but fast on the fourth day and the Preparation (Friday). Neither pray as the hypocrites; but as the Lord commanded in His Gospel, thus pray: Our Father who art in heaven, hallowed be Your name. Your kingdom come. Your will be done, as in heaven, so on earth. Give us today our daily (needful) bread, and forgive us our debt as we also forgive our debtors. And bring us not into temptation, but deliver us from the evil one (or, evil); for Yours is the power and the glory forever. Thrice in the day thus pray.

Now concerning the Thanksgiving (Eucharist), thus give thanks. First, concerning the cup: We thank you, our Father, for the holy vine of David Your servant, which You made known to us through Jesus Your Servant; to You be the glory forever. And concerning the broken bread: We thank You, our Father, for the life and knowledge which You made known to us through Jesus Your Servant; to You be the glory forever. Even as this broken bread was scattered over the hills, and was gathered together and became one, so let Your Church be gathered together from the ends of the earth into Your kingdom; for Yours is the glory and the power through Jesus Christ forever. But let no one eat or drink of your Thanksgiving (Eucharist), but they who have been baptized into the name of the Lord; for concerning this also the Lord has said, Give not that which is holy to the dogs.

**This is followed by a prayer and a discourse on teachers, apostles and prophets. Then there follows a section on reception of Christians and support of prophets.*********************************

But every Lord's day gather yourselves together, and break bread, and give thanksgiving after having confessed your transgressions, that your sacrifice may be pure. But let no one that is at variance with his fellow come together with you, until they be reconciled, that your sacrifice may not be profaned. For this is that which was spoken by the Lord: In every place and time offer to me a pure sacrifice; for I am a great King, says the Lord, and my name is wonderful among the nations.

Therefore, appoint for yourselves bishops and deacons worthy of the Lord, men meek, and not lovers of money, and truthful and proven; for they also render to you the service of prophets and teachers. Despise them not therefore, for they are your honored ones, together with the prophets and teachers. And reprove one another, not in anger, but in peace, as you have it in the Gospel; but to every one that acts amiss against another, let no one speak, nor let him hear anything from you until he repents. But your prayers and alms and all your deeds so do, as you have it in the Gospel of our Lord.

Watch for your life's sake. Let not your lamps be quenched, nor your loins unloosed; but be ready, for you know not the hour in which our Lord comes. But often shall you come together, seeking the things which are befitting to your souls: for the whole time of your faith will not profit you, if you be not made perfect in the last time. For in the last days false prophets and corrupters shall be multiplied, and the sheep shall be turned into wolves, and love shall be turned into hate; for when lawlessness increases, they shall hate and persecute and betray one another, and then shall appear the world-deceiver as the Son of God, and shall do signs and wonders, and the earth shall be delivered into his hands, and he shall do iniquitous things which have never yet come to pass since the beginning. Then shall the creation of men come into the fire of trial, and many shall be made to stumble and shall perish; but they that endure in their faith shall be saved from under the curse itself. And then shall appear the signs of the truth; first, the sign of an outspreading in heaven; then the sign of the sound of the trumpet; and the third, the resurrection of the dead; yet not of all, but as it is said: The Lord shall come and all His saints with Him. Then shall the world see the Lord coming upon the clouds of heaven.

see https://www.newadvent.org/fathers/0714.htm