‘I was in Spirit on the Lord's day.'
The phrase ‘in Spirit' refers in Revelation to the work of the Spirit in bringing John to a specific point or place so that he may receive a vision, moving backwards and forwards in space and time (Revelation 4:2; Revelation 17:3; Revelation 21:10). Compare also Ezekiel in Ezekiel 3:12; Ezekiel 3:14; Ezekiel 8:3; Ezekiel 11:1; Ezekiel 11:24; Ezekiel 37:1; Ezekiel 43:5.
‘On the Lord's day.' This is the only occasion where such a phrase is connected with being ‘in the Spirit'. And this suggests that it is not just a reference to the day on which it happened, for that is never considered important anywhere else, but rather to a reference to where the Spirit took him. Thus we must question whether it means what we call ‘Sunday'.
Sunday is not called ‘the Lord's day' (he kyriake hemera) anywhere in Scripture, and as far as we know the term was not elsewhere used in that way until the early second century, when it was possibly by mistaken implication from this book. In fact the technical term in the New Testament for what we call Sunday was ‘the first day of the week'. This was true when 1 Corinthians was written (1 Corinthians 16:2) and also when Luke was writing (Acts 20:7).
So in view of the fact that the phrase ‘in the Spirit' occurs three times more in Revelation (Revelation 4:2; Revelation 17:3; Revelation 21:10), in each case when John is introduced to particular revelations, it seems certain that this phrase here refers to such a revelation and this would suggest that the phrase ‘the Lord's day' parallels to some extent references to ‘the day of the Lord', that great day when God would act to bring about His final purposes.
But the change of phraseology prevents direct connection. Had John meant ‘the day of the Lord' he would have said so. While in Hebrew, and therefore in the Old Testament, a phrase directly parallel to ‘the Lord's day' is not linguistically possible, it would have been possible in the New. But when the phrase ‘the day of the Lord' also occurs in the New Testament, as it often does, it is always in the same form as in the Old Testament. It is a technical term directly imitating the Hebrew. Thus had he meant that John would have used it here.
The fact is that in the New Testament ‘the Lord's' always means ‘Christ's'. Compare for this ‘the Lord's supper' (1 Corinthians 11:20), and also see 1Co 7:22; 1 Corinthians 10:21; 1 Corinthians 11:26; 1 Corinthians 11:29; Galatians 1:19. So this is rather referring to ‘the Lord Christ's day', for which compare 1 Corinthians 1:8; 1 Corinthians 5:5; Philippians 1:6; Philippians 1:10; Philippians 2:16. This is confirmed by the immediately following vision of Christ as about to act on His day.
So in this vision John is transported to ‘Christ's day' or, as he puts it literally, ‘the Lord's day', to the time when the Lord Christ is about to have His day, the day awaited from the beginning of time.
This is in contrast with the present time. At present it is ‘man's day' (1 Corinthians 4:3 - which is of similar construction) rather than the Lord's day (1 Corinthians 4:5). But that is now about to pass and man will learn at Christ's return that man has had his day. So John is brought face to face with the glorified Christ at the point when He is ready to bring this age to completion and to carry out the final judgment.
The Day of Christ differs from the Day of the Lord in that the former refers to the day in terms of Christian accountability whereas the latter refers to the time of God's judgments on the world, although this latter signifies more than that for it culminates in the new Heavens and the new earth (2 Peter 3:10-13) connecting the two. But John's message is specifically to Christians and he is concerned to refer the day specifically to them so that it is ‘Christ's day' that he refers to.
It should be noted that this reference to time refers only to this particular vision. There are therefore no specific grounds for referring the phrase ‘the Lord's day' to any other visions in Revelation, for they move backward and forward in time.
The significance of this first vision is to remind the churches that Christ is coming, that the day of Christ is imminent, and that He is, as it were, poised on the point of returning for His people, something which will encourage them in what lies ahead. It is to remind them that they must therefore be in readiness for that Coming.
Later in Revelation 19 that coming will be described in terms which clearly connect with this vision. So in vision John is taken forward in time (he was not aware of how long it would be) so that he can report back to the churches that he has seen the glory of the Coming One for Whom they are waiting, standing as it were at the gate, ready to return, thus stressing the imminence of His return.