Revelation 1:10

The Holy Spirit appears to have caught John up and projected him in his spirit to a future time in a vision (cf. Revelation 4:2; Revelation 17:3; Revelation 21:10; Ezekiel 3:12; Ezekiel 3:14; Ezekiel 8:3; Ezekiel 11:1; Ezekiel 11:24; Ezekiel 43:5). [Note: See F. J. A. Hort, The Apocalypse of St. John, p. 15.]

The "Lord’s day" probably refers to Sunday. [Note: Swete, p. 13; Morris, p. 51; Newell, p. 24; Johnson, pp. 424-25; Mounce, p. 76; Beasley-Murray, p. 65; Aune, p. 84; Ladd, p. 31; Beale, pp. 203-4; Roger T. Beckwith and Wilfred Stott, This is The Day: The Biblical Doctrine of the Christian Sabbath in its Jewish and Early Christian Setting.] But it could refer to the future day of the Lord spoken of frequently elsewhere in Scripture. [Note: E. W. Bullinger, The Apocalypse or "The Day of the Lord," p. 152; Walvoord, p. 42; Smith, p. 324.] The New Testament writers never called Sunday the Lord’s day elsewhere in Scripture. This term became common after the apostolic age. [Note: Thomas, Revelation 1-7, p. 91.]

A loud trumpet-like voice instructed John to write down what he saw and send it to seven churches in Asia Minor. The trumpet reference probably implies that submission to its command was necessary. The voice belonged to Jesus Christ (Revelation 1:12; Revelation 1:17-18).