Revelation 11:17
Saying, We give thee thanks, O Lord God Almighty, which art, and wast, and art to come; because thou hast taken to thee thy great power, and hast reigned. Saying, We give thee thanks, O Lord God Almighty, which art, and wast, and art to come; because thou hast taken to thee thy great power, and hast reigned.
The thanksgiving comes after the seventh angel sounds, when loud voices in heaven announce that the kingdoms of this world have become the Lord's and His Anointed's, who will reign forever. Its speakers are the twenty-four elders falling facedown in worship, and in that posture they represent the faithful and obedient giving thanks to God. They give thanks to the eternal all-powerful Lord, who is and was and is to come, because He has taken to Himself His great authority and has begun to reign.
The taking of His great power is Christ assuming His authority to rule at His second coming to this world. It does not describe the present kingdom of grace now being built day by day as hearts full of sin and rebellion yield to the sovereignty of His love, but the complete establishment of the kingdom of glory. At that time the kingdom and dominion under the whole heaven is given to the people of the saints of the Highest, who inherit the kingdom prepared for them from the foundation of the world.