What did John mean by the "Lord's Day"? When did the prophet receive his vision? As scholars look at this text, they don't find the question easy to answer. They offer at least five plausible options. First is the day we call Saturday. Saturday is the seventh day of the week on the Hebrew calendar, known to the Jews as the Sabbath. Scripture frequently refers to the Sabbath as "the Lord's Day." In Isaiah 58 the Lord Himself speaks of the Sabbath as "my holy day." And in Mark 2:27, 28 Jesus declares that He is "Lord of the Sabbath." So a strong biblical option for understanding John is that he was alluding to these earlier texts to identify the Sabbath as the day on which the vision came. Since he shows a great deal of interest in the Sabbath command in chapter 14, I believe this is the best option.
The second option is the day now named Sunday. Christian writings from the second century (as close as 35-40 years after the book of Revelation) clearly use the phrase "the Lord's Day" as a figure of speech for Sunday. The idea developed in relation to the fact that Jesus rose from the dead on the first day of the week (our Sunday), so "the Lord's Day" could allude to that. But we have no evidence that Christians in the first century kept Sunday.
A third possibility is that John was referring to what we regard as Easter. Jesus rose on Sunday, the first day of the week. But it was also at the time of the Jewish Passover. Christians celebrate Easter every year around the time of Passover. If that is what the prophet had in mind, he is telling us he received the vision in the spring, around Passover season.
Fourth, perhaps John had in mind the Old Testament Day of the Lord, a phrase used in the Bible for God's great intervention at the end of earth's history. In this case the revelator would be saying something like "I saw this vision with the end of the world in mind."
Fifth, some ancient documents suggest a special "Emperor's Day" once a year, when people would gather for worship. John might be "thumbing his nose" a bit at the Roman emperor by asserting that God intervened on the very day when the enemy seemed in full control. Revelation shows that Jesus is Lord, not a human emperor.
At a moral spiritual level, it doesn't hurt to remind ourselves that every day is a gift from God. Every day is a day "that the Lord has made" (Ps. 118:24), a time to be used to glorify Him and to bless others. Every day is to be enjoyed with thanksgiving. Have a good one today!
Lord, You have given this day to me. I return it to You with my thanks. I dedicate all my thoughts and actions to Your service.