The Catechism in Questions & Answers

641. What do we mean when we say: “For Yours is the kingdom and the power and the glory forever”?

These words are an expression of praise to God (doxology). They serve to glorify the Almighty God, and He thereby receives the glory He is due. Our view is hereby also directed to the completion of His plan of salvation, when the redeemed will be permitted to experience the glory of God in His presence forever.

Plan of salvation: see Questions 243. et seq.