4:1 After this. “After this” means, after all that was revealed concerning the church age, as represented by the seven church epistles. Thus, John is now carried forward, in the Spirit, to see the events that will take place next. God, who created time as well as space, is Himself transcendent to both time and space, and thus could easily translate John in both space and time—in space to heaven, and in time to the future. John, therefore, was able to see and hear these amazing events of the future as an actual eye-witness, just as we shall eventually see and hear them ourselves when we, like John, are caught up into heaven to be with the Lord (I Thessalonians 4:16-17).
4:1 trumpet. When the Lord finally opens the heavenly doors (compare Revelation 3:8,20) and raptures all true Christians, saying in effect “Come up hither,” it will indeed be with the voice of a trumpet heard all over the world at once (note I Corinthians 15:52; I Thessalonians 4:16).
4:1 things which must be hereafter. In Revelation 4–22, the Lord shows us, through John’s eyes, the “things which must be hereafter”—that is, after the church age (see the outline given in Revelation 1:19, where similar wording is used). In the original Greek, this verse both begins and ends with the phrase “after these things.” The church age (“the things which are”) is not discussed after Revelation 3.