The Lord's day - Rev 1:10

Question: When we read Lord's day as in Rev 1:10, does this mean His appointed time as in Lev 23 or any particular event?

This is a good question, particularly since the Lord's day has become a common reference to Sunday among English speaking Christians.  As such, Rev 1:10 has become one of three or four NT passages used as proof texts for the assertion that the Church had abandoned Shabbat observance before the end of the first century.  However, this conclusion is the result of rather superficial reasoning.  The expression on the Lord's day is a translation of εν τη κυριακη  ημερα.  This expression occurs only here in the NT.  The exact phrase the day of the Lord (various forms of ημερα κυριου) occurs 6 times in the rest of the NT writings:

Acts 2:20         … before the great and glorious day of the Lord shall come (Joel 2:31)

1 Cor 1:8         … who shall also confirm you to the end, blameless in the day of our Lord Yeshua.

1 Cor 5:5         I have delivered such a one to Satan for the destruction of the flesh in order that the spirit might be saved in the day of the Lord.

1 Thes 5:2        For you yourselves know that the day of the Lord will come like a thief in the night.

2 Thes 2:2        … that you may not be quickly shaken from your composure or be disturbed either by a spirit, a message, or a letter as if from us as if the day of the Lord had come.

2 Pet 3:10        But the day of the Lord will come like a thief…

There is no exact equivalent to κυριακη  ημερα in the Hebrew scriptures, but Isaiah 58:13 is close.  This passage asserts that Shabbat is the special holy day of YHWH, and YHWH promises blessing to those who keep Shabbat holy.  Hebrew translations of Rev 1:10 render the expression κυριακη  ημερα by יום האדון or by יום יהוה.  The phrase יום האדון does not occur in the Hebrew bible, but יום יהוה occurs 15 times in the latter prophets.  Every time it occurs it is a reference to the climatic visitation of YHWH to execute judgment both on Israel and on the nations as a whole.  As indicated by the above NT references, this meaning was brought into the NT without change.

Consequently, my conclusion concerning the meaning of εν τη κυριακη  ημερα in Rev 1:10 is the following:  John did not use the expression the day of the Lord because he was referring to a specific day in his time, not the coming future time of God's judgment on the world, which the book of Revelation itself indicates is still to come in the future.  Also, there is no evidence to indicate that the expression the Lord's day in English translations of Rev 1:10 has anything in common with the modern use of the same expression.  This leads me to think that John was referring to a Shabbat day as suggested by Isaiah 58:13.  The implication of this conclusion is that all Christian churches that have substituted Sunday for Shabbat are being disobedient to the revealed will of God.