Catechism of the Catholic Church
a, b, c, and e. Para. 1173: When the Church keeps the memorials of martyrs and other saints during the annual cycle, she proclaims the Paschal mystery in those "who have suffered and have been glorified with Christ. She proposes them to the faithful as examples who draw all men to the Father through Christ, and through their merits she begs for God's favors" (SC 104; cf. SC 108, 111).
Para. 1195: By keeping the memorials of the saints—first of all the holy Mother of God, then the apostles, the martyrs, and other saints—on fixed days of the liturgical year, the Church on earth shows that she is united with the liturgy of heaven. She gives glory to Christ for having accomplished his salvation in his glorified members; their example encourages her on her way to the Father.