What is the mystery of God that is finished at the seventh Trumpet?

Revelation 10 records a mighty angel declaring that there should be time no longer, and that in the days of the voice of the seventh angel, when he begins to sound, the mystery of God should be finished, just as He had declared to His servants the prophets. This is not simply a statement about the end of delay in judgment, but a pointer to something that reaches its completion at that exact moment.

Colossians 1:26-28 identifies that mystery directly: it is the mystery hidden from ages and generations but now made known to the saints, namely Christ in you, the hope of glory. Paul describes preaching this mystery so that every believer might be presented perfect in Christ Jesus. This is the riches of the glory of Christ dwelling in and among His people, and it is this very mystery, the full revelation and glorification of the Body of Christ, that reaches its finished state at the seventh trumpet.

This means that up through Revelation chapter 10, while the sixth trumpet is still sounding, the Church remains on the earth, still hoping and waiting for that fulfillment. Revelation 6:9-11 confirms this, showing that fellow servants and brethren are still on the earth to be killed by the Antichrist during this time, which would not make sense if the mystery, the completion of the Church, had already been finished earlier in the visions. The mystery is not finished until the seventh trumpet sounds, marking the true last trump and the completion of God's redemptive work in His people.

So the mystery of God finished at the seventh trumpet is the culmination of Christ in you, the hope of glory, that is, the full and final glorification of the saints, the Body of Christ being brought to completion exactly as declared beforehand to His servants the prophets.