The book of Revelation of St. John, read in the Church's liturgy, first reveals to us, "A throne stood in heaven, with one seated on the throne": "the Lord God." It then shows the Lamb, "standing, as though it had been slain": Christ crucified and risen, the one high priest of the true sanctuary, the same one "who offers and is offered, who gives and is given." Finally it presents "the river of the water of life . . . flowing from the throne of God and of the Lamb," one of most beautiful symbols of the Holy Spirit.
-- CCC 1137