NOTES for Rev 1:10
John's visions, set out in the Book of Revelation, begin with the fact that, by his own testimony, he "was in the Spirit on the Lord's day" (as the Greek text has it). The expression "the Lord's day" in this context can be understood in different ways. The first thing that comes to mind is that it refers to Sunday, which the first Christians celebrated roughly as we celebrate it today, above all with solemn worship. But it must be admitted that today it is practically impossible to say exactly whether Christians at the end of the first century A.D. (when the Book of Revelation was written) celebrated this day in that way or not. Another explanation appears no less plausible: it refers to the feast that was called "the day of Yahweh" (or "the Lord's day") even before the exile, in the era of the First Temple. Apparently, at that time it was celebrated around the same days as Yom Kippur and Rosh Hashanah ("the Jewish New Year").
Originally, the day of Yahweh was probably the day of the consecration of the First Temple, which may have taken place precisely on the first day of the year. No references to this feast have survived from the postexilic period, but perhaps John's words are evidence that it did not disappear. If so, the revelation John received proves significant also because of the day on which it was given. It was no accident that the day of Yahweh was marked with special solemnity even in the days of the First Temple: this day was the day of the triumph of God and the Kingdom of God, the day of Yahweh's solemn ascent to the throne, after which the day of Judgment properly begins and the world becomes the Kingdom of God. It was no accident that the liturgical experience of visions of the throne of glory, reflected in Yahwistic hymnography and especially in the Book of Psalms, was connected with the worship of that day.
And John receives his revelation when the Temple no longer existed and the former history had come to an end, leaving both the Synagogue and the Church in deep bewilderment and spiritual confusion: everything ended not quite as, or not at all as, both Jews and Christians expected. Christians in particular could not understand why, more than ten years after the destruction of the Temple predicted by Jesus, He had not returned as He promised. And the revelation received by the apostle answered this question that tormented many, whose meaning came down to this: earthly history had truly ended, but the history of the Kingdom entering the world was only beginning. And the fact that this new history was spiritually inseparable from the former one was emphasized by the fact that it was given on the day of Yahweh, on the day of the old temple feast whose very meaning was the expectation of the imminent triumph of the Kingdom. Thus the old age was spiritually joined to the new.