-- Jer 14:17-22
The Revelation of "what must soon take place," the Apocalypse, is borne along by the songs of the heavenly liturgy but also by the intercession of the "witnesses" (martyrs). The prophets and the saints, all those who were slain on earth for their witness to Jesus, the vast throng of those who, having come through the great tribulation, have gone before us into the Kingdom, all sing the praise and glory of him who sits on the throne, and of the Lamb. In communion with them, the Church on earth also sings these songs with faith in the midst of trial. By means of petition and intercession, faith hopes against all hope and gives thanks to the "Father of lights," from whom "every perfect gift" comes down. Thus faith is pure praise.
-- CCC 2642