“I was in the spirit on the Lord’s Day…”
John was in exile on the Isle of Patmos, and he was in the spirit on the “Lord’s Day.” Exactly what day is that?
Some will say the “Lord’s Day” is the first day of the week—Sunday. Others insist it is the seventh day of the week—Saturday.
What do the scriptures have to say?
That the Church, as early as the days of the apostles, worshipped on the first day of the week (which they called "The Lord's Day") is indesputable.
Acts 20:7 they gathered, had communion and preached on the first day of the week. In 1 Corinthians 16:2 we see them gathering and taking up offerings on the
first day of the week.
These things are still done when we gather together for corporate worship. The scriptures show the first Christians gathering on the first day of the week.
Revelation 1:10 The first day of the week became the "Lord's Day" because that is the day Jesus, The Lord of the Sabbatah, rose from the dead, and the Body of Christ began honoring that day immediately—not, as some so loudly claim, in the fourth century when Christianity became the official religion of Rome.
However, there were disputations about it even then, and Paul assured everyone that which-ever day they preferred to honor was OK—Romans 14:5—as every day should be holy unto the Lord.