Why do people assume Rev. 1:10 is speaking of Sunday ? "I was in the Spirit on the Lord's day, and heard behind me a great voice, as of a trumpet". No day of the week is mentioned. Some believe this refers to Sunday, while others believe this has to do with the “Day of the Lord”. This passage has been wrongly translated in the KJV. It should read, “I was by the Spirit in the Day of the Lord…” The Greek words used and translated “The Lord’s Day”, are the same as used in 1 Thes 5:2; 2 Thes 2:2; 2 Pet 3:10 and are properly translated the “Day of the Lord” in all of the these other passages. These Greek terms are equivalent to the Hebrew “Day of the Lord” in Isa 2:12; 13:6,9; Joel 2:11, etc. As for the preposition "on" (on the Lord's day), the Greek "en" means "in". So this passage is NOT saying John was in the spirit on Sunday, but that he was taken by the Spirit into the future, into that great and terrible Day of the Lord.