It remains for us to define the meaning of the "Lord’s Day" of Revelation 1:10 solely in the light of the text, context, and the teaching of the New Testament. Assuming that the Seer intended to specify that on a Sunday he found himself rapt in the Spirit, would he have designated such a day as “Lord’s Day”? Because in the New Testament, this day is always called “the first day of the week,” is it not strange that in this one place, the writer would use a different expression to refer to the same day?
More important still, if, as many exegetes maintain, John the Apostle wrote at approximately the same time both the Revelation and the fourth Gospel, then would it not seem reasonable to expect him to employ the same expression even in his Gospel, especially when reporting the first-day events of the resurrection and appearances of Jesus (John 20:1, 19, 26)? In the apocryphal Gospel of Peter, written several decades later, we notice for instance that the day of the resurrection is designated not as the “first day of the week” but as “Lord’s—kuriake” since the latter had by then become the term commonly used. If Sunday had already received the new appellation “Lord’s Day” by the end of the first century when both the Gospel of John and the book of Revelation were written, we would expect this new name for Sunday to be used consistently in both works, especially since they were apparently produced by the same author at approximately the same time and in the same geographical area. If a new term prevails and is more readily understood, a writer does not confuse his readers with archaic time designations.
On another historical note, in the second century, Christians were trying to figure out how much of Judaism to get rid of, not because there was a biblical mandate to keep the first day of the week, but predominantly because of the Jewish upheavals that occurred-AD 70, AD 118, AD 135-that lead to the Jews losing their legal privileges in the empire. They were trying to distance themselves from the backlash against Jews, seeing as how Christians and Jews worshipped on the same day. A gradual shift occurred, predominantly in the major cities. Shortly after the Barcopa Rebellion of AD 135, you will find language in the Epistle of Barnabas, circa AD 135-140, attempting to distinguish Christians from Jews; however, the vast majority of Christians worshipped on the seventh-day Sabbath. There is no New Testament language calling the first day of the week Sabbath, but the seventh day is consistently referred to as the Sabbath. There is no commandment changing the Sabbath from the seventh day to the first day. Just because later Christians honored Sunday, does not mean that one can anachronistically refer to the first day in scripture as the Lord's Day. There are many areas of the Church's teachings that have diverged greatly from the teachings of the New Testament. The Sabbath is but one. Protestant reformers were integral in bringing attention to the many points of deviation from scripture brought about throughout the centuries after the apostles, and are continuing to rediscover the faith of Jesus. Sunday worship is something that the later church adopted, despite there being no Biblical foundation for it; however, that is not the question. The question is, "What determines the rule of life, the traditions of the church, or the scriptures themselves? If the answer is "tradition," then it does not matter which day we superimpose upon the commandment to "Remember the Sabbath day to keep it holy.." Exodus 20:11. We can just as easily keep Tuesday as holy. If, however, we follow Scripture alone, then there is but one day that is consistently called the Sabbath, the seventh day.
This whole change from Sabbath to Sunday still does not apply to the issue in question, Revelation 1:10. Sunday is consistently referred to as "the first day of the week in the NT. None of John's writing exalts Sunday as the new Sabbath. The immediate context which precedes and follows Revelation 1:10 contains unmistakable references to the eschatological day of the Lord. In the preceding verses Christ is portrayed as the One who “is coming with clouds, and every eye will see him” (v. 7) and as the One “who is and who was and who is to come (v. 8). In the following verses John describes the vision of the glorious and triumphant “Son of Man” who has“the keys of Death and Hades” (vv. 12-18). The same “Son of Man” appears again later to John with “a sharp sickle in his hand... for the harvest of the earth” (14:14, 15), where unquestionably the reference is to a future time of judgment. The immediate context is clearly eschatological. This suggests that John felt himself transported by the Spirit to the future glorious day of the Lord.
Additional support for this interpretation is provided by the fact that John mentions twice again the day of judgment and of Christ’s coming, and in each instance, he uses a somewhat different expression: “the great day of God—tes hemeras megales tou theou” (16:14) and “the great day of wrath— he hemera he megale tes orges” (6:17).
These variations in the designation of the day of Christ’s coming indicate that the event was of such great importance that it could be designated in a great variety of ways without the risk of being misunderstood. No less than thirty times John refers explicitly to it in his book. In the New Testament, in fact, the day of Christ’s coming, which is regarded as the foundation and consummation of the Christian faith, hope, and living, is described by a wide variety of expressions, such as “the day of judgment,” “the day,” “that day,” “the last day,” “the great and notable day,” “the day of wrath and revelation,” “the day of our Lord Jesus Christ,” “the day of Christ,” “the day of the Lord,” “the great day,” and “the great day of God.” Christ himself calls the day of His coming “his day—hemera autou” (Luke 17:24). The fact that such a broad diversity of expressions is used to name the day of Christ’s coming, and the fact that John himself refers to it with different appellatives, make it altogether plausible that “the Lord’s day” is simply one of the many different designations for the same event.