Please explain the significance of “7” in Revelation, specifically where it speaks of seven angels and when the seventh angel said, “It is done.”
Revelation is steeped in signified language (Rev. 1:1, KJV), so one should interpret the numbers within the book symbolically, not literally. The best way to figure out the symbolism is to primarily go to the rest of the Bible as guidance (2 Tim. 4:2).
Scripture shows that “7” symbolizes completeness. For example, “for three and for four” is a symbolic way of saying something was complete in God’s sight (Amos 1:3, 6, 9, 11, 13; 2:1, 4, 6; Prov. 30:15b, 18, 21, 29). Israel was told to march around Jericho seven times on the seventh day before the walls fell (Josh. 6:4-5). Naaman was told to baptize himself in the Jordan seven times before his leprosy would be cured (2 Kings 5:14). God’s Word was called “pure” while being compared to “silver refined in a furnace on the ground, purified seven times” (Ps. 12:6). Jesus commanded forgiveness to be done “seventy times seven” times, i.e., completely (Matt. 18:21-22). On the seventh day creation was said to be completed and God rest (Gen. 2:1-2).
John saw three visions in Revelation which were very similar in nature: a vision of seven seals (6:1-17; 8:1-5), a vision of seven trumpets (9:6-13; 9:1-21; 11:15-19), and a vision of seven plagues (15:1-8; 16:1-21). All of them cover the same time period: the entirety of the Christian age. Each of them examines from different perspectives the Christian age through judgment and into eternity.
Concerning the angels, in the vision of the seven trumpets we see seven angels each blow a trumpet which then ushers in a part of the vision which symbolically foretells of a spiritual hardship Christians will deal with throughout the Christian age and into eternity. In the vision of the seven plagues we see seven angels each pour a bowl of plague upon the earth, each of which ushering in a part of the vision which symbolically foretells of the torments suffered by people who do not submit their lives to God’s will in the Christian age through judgment and into eternity.
The seventh angel pouring the seventh bowl of plague upon the earth takes us to the part of the vision which symbolically foretells of judgment and eternity (16:17-21). The passage actually insinuates rather strongly that God, rather than an angel, is the One who says “It is done!” (“a loud voice came out of the temple, from the throne, saying, ‘It is done!’”). He says this after the seventh angel pours his bowl into the air, which further study shows is a figurative description of the final, eternal punishment waiting for those following false religions who did not submit to God. So when the seventh angel pours the seventh plague (which represents the eternal punishment of the wicked) and God says, “It is done!”, that means that His plan for man at this point has been completed (the symbolic meaning of “7”).
Each of the parallel visions in Revelation – the seven seals, the seven trumpets, and the seven plagues – all cover the same period of time: the totality of the Christian age going through judgment into eternity. In each of them when the seventh seal, trumpet, and plague are talked about, John gives a symbolic description of judgment and the beginning of eternity, thus showing the completion of God’s dealings with man here on earth in this life and age.