Should we observe the Sabbath (Saturday), or the Lord’s Day (Sunday)?
In the very early Church, Christians knew the right answer:
Further, He says to them, “Your new moons and your Sabbaths I cannot endure.” Ye perceive how He speaks: Your present Sabbaths are not acceptable to Me, but that is which I have made, [namely this,] when, giving rest to all things, I shall make a beginning of the eighth day, that is, a beginning of another world. Wherefore, also, we keep the eighth day with joyfulness, the day also on which Jesus rose again from the dead. And when He had manifested Himself, He ascended into the heavens.
~Epistle of Barnabus (c. 80 A.D.)
those who were brought up in the ancient order of things have come to the possession of a new hope, no longer observing the Sabbath, but living in the observance of the Lord’s Day
~ Ignatius (c. 107 A.D.)
The Didache – Chapter 14.
Christian Assembly on the Lord’s Day
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.
~ The Didache (c. 120 A.D.)
But the Gentiles, who have believed on Him, and have repented of the sins which they have committed, they shall receive the inheritance along with the patriarchs and the prophets, and the just men who are descended from Jacob, even although they neither keep the Sabbath, nor are circumcised, nor observe the feasts.
~ Justin Martyr (c. 150 A.D.)
And on the day called Sunday, all who live in cities or in the country gather together to 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 verbally instructs, and exhorts to the imitation of these good things. Then we all rise together and pray, and, as we before said, 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; and 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. And they who are well to do, and willing, give what each thinks fit; and what is collected is deposited with the president, who succours the orphans and widows and those who, through sickness or any other cause, are in want, and those who are in bonds and the strangers sojourning among us, and in a word 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 wrought a change in the darkness and matter, made the world; and Jesus Christ our Saviour on the same day rose from the dead.
~ Justin Martyr (c. 150 A.D.)
For in respect of the observance of the eighth day of the Jewish circumcision of the flesh, a sacrament was given beforehand in shadow and in usage; but when Christ came, it was fulfilled in truth. For because the eighth day, that is, the first day after the Sabbath, was to be that on which the Lord should rise again, and should quicken us, and give us circumcision of the spirit, the eighth day, that is the first day after the Sabbath, and the Lord’s Day, went before in the figure; which figure ceased when by and by the truth came and spiritual circumcision was given to us
~ Cyprian (c. 250 A.D.)