Glory be to the Father, and to the Son, and to the Holy Spirit, as it was in the beginning, is now and ever shall be, world without end. Amen. This short prayer of praise known as the Glory Be comes at the end of each decade, but it is not simply a closing prayer. Rather it is meant to express the peak of our contemplation. Praise of the Holy Trinity is the Christian response to the events of salvation that God has accomplished in his Son. We praise God for his becoming man and dwelling among us; for his death, which conquered sin; for his resurrection, which gives us new life; for his ascension to the right hand of the Father; and for sending the Holy Spirit to us at Pentecost (CCC, 2641).
—from the book Praying the Rosary Like Never Before: Encounter the Wonder of Heaven and Earth by Edward Sri