Colossians makes reference to this:
I now rejoice in my sufferings for you, and fill up in my flesh what is lacking in the afflictions of Christ, for the sake of His body, which is the church, of which I became a minister according to the stewardship from God which was given to me for you, to fulfill the word of God, the mystery which has been hidden from ages and from generations, but now has been revealed to His saints. To them God willed to make known what are the riches of the glory of this mystery among the Gentiles: which is Christ in you, the hope of glory.
There is a competing mystery referenced in scripture also, which is called the mystery of iniquity, or the mystery of lawlessness, which is in reference to the "sinful kingdom" of the Antichrist power. (See 2 Thessalonians 2:7 and Revelation 17:5)
The Bible presents us with two competing spiritual kingdoms or paths.
Do you not know that to whom you present yourselves slaves to obey, you are that
one’s slaves whom you obey, whether of sin leading to death, or of obedience
leading to righteousness?
Both of these are also likewise represented as leaven which pervades the being and influences the entire person.
Thus, the mystery of lawlessness is the principle of sin in the heart, and the mystery of God is the antithesis to this: namely, the leaven of the Spirit which produces righteousness in the heart.
And so, when the seventh trumpet sounds, the leaven is finished working, and it's time to take the bread out of the oven. The spreading and multiplying of righteousness has finished, and there is nothing more to be done.