John tells us that he was on the Isle of Patmos “for the word of God, and for the testimony of Jesus Christ” (vs. 9) He was very aged and the last remaining apostle, having outlived all the others, nearly all of whom died horrible deaths, also “for the word of God, and for the testimony of Jesus Christ” they faithfully bore witness to, to the death. What Jesus had foretold of John had proven true: John would tarry (John 21:22-23). All the others died, but John remained. And he remained waiting. Then the risen Lord Jesus spoke to John through his angel, while John the aged continued tarrying on the Isle of Patmos.
However, you read too much into the account when you comment, “The aged John didn't seem to be fazed by the sudden appearance.” No, he fell at the feet of the risen Christ “as if dead” (vs. 17)!
Well, the question of what significance there is to the voice John heard being loud, and being behind him… The answer begins with grasping what it meant for John “to be in the Spirit” prior to hearing this loud trumpet sound behind him. Matthew Henry, in his Commentary states:
“4.The frame that his soul was in at this time: He was in the Spirit.
He was not only in a rapture [caught up] when he received the vision,
but before he received it; he was in a serious, heavenly, spiritual
frame, under the blessed gracious influences of the Spirit of God. God
usually prepares the souls of his people for uncommon manifestations
of himself, by the quickening sanctifying influences of his good
Spirit.” (page 1983 column 1)
This means that the sound he suddenly heard was a heavenly sound, far greater than any mere earthly trumpet sound could be. Even the attention-grabbing shofar sound of the instruments used by God’s people would likely be feeble compared with this clarion-call from heaven. Our modern-day metal trumpets are far more crisp and loud than trumpets of old, yet even the stage of the Royal Albert Hall in London, filled with trumpet players at full volume, in the superb acoustics of that ‘temple’ to music, could never approach that trumpet sound from heaven.
It came from behind John. His spiritually attuned ‘ears’ of faith enabled him to detect from what direction the heavenly sound came, and – his attention being secured – now his spiritual sight needed to be engaged. For what John now needed to see was the heavenly perspective of what Christ was seeing with regard to his engagement with the church in the world, and the worldly events to unfold, that no mere human vision could begin to ‘see’.
The Revelation of Christ that then unfolded had to be recorded in written form by John, for others to read, to believe, and to be blessed thereby. Christ later speaks of those who hear his voice hearing what the Spirit saith unto the churches” (Rev. 3:20-22). Because John first heard, saw, and wrote down, those who are members of the Church Christ builds, which the gates of Hades can never overcome, can also ‘hear’ and ‘see’ spiritually what John heard and saw. But in order to write down what was heard and what was seen in astounding visions, John had to turn around and look behind him. So with all who belong to Christ by faith. Where we are physically located continually grabs our attention, with all the worldly sounds and sights invading us, trying to distract us from what we REALLY need to hear, and to see – not in front of us, but that which is behind and above us.
Christians need to hear, and turn around. Only then will we, too, see spiritually what we have heard spiritually. John heard the unearthly sound behind him and turned to then see the significance of that call to attention. May it be so with all believers who know that the clamour and chaos of this world would prevent us turning away from it to grasp how our Lord is sovereignly dealing with his Church and this ungodly world to bring all things to its climax, as John recorded. Unless we grasp the amazing significance of this last canonical book, we will be unprepared for heaven’s plagues being poured out in judgment, confused by it all, because we are not hearing and seeing as did John.