In verses nine and ten John identifies his exact circumstances when the Lord began to reveal all that is recorded in this staggering book.
9 I John, who also am your brother, and companion in tribulation, and in the kingdom and patience of Jesus Christ, was in the isle that is called Patmos, for the word of God, and for the testimony of Jesus Christ.
10 I was in the Spirit on the Lord's day, and heard behind me a great voice, as of a trumpet,
John says four key things:
He essentially begins by saying, “This is me, John, yes, the same guy that has fellowshipped with you in Christ in all that it has demanded of all of us; It’s me!”
He then reminds his hearers that he was exiled on the island of Patmos because of his open testimony to Caesar regarding Who Jesus Christ truly is.
He speaks then of being “in the Spirit on the Lord’s day.” Clearly he is identifying that he was seeking the direct guidance of the Holy Spirit; additionally he suggests the significance of the Lord’s day [Sunday] as a day of worship.[1]
Finally, he makes it clear that under these circumstances he heard behind him “a great voice, as of a trumpet.” This plainly suggests that this trumpet-like voice emphatically “got his attention.”
[1] Not all commentators hold the view that John is referring to the first day of the week here [Sunday]. Some hold that John is referring to “the day of the Lord,” spoken of throughout the Bible.