As the prayers themselves witness, the Church teaches us that we should pray not only directly to God, but also to those who are close to God, those who have the power to intercede upon our behalf. Indeed, we pray to the angels to help and watch over us; we pray to the saints in heaven to ask their intercession and assistance; we pray to the Blessed Mother to enlist her aid, to ask her to beg her Son to hear our prayers. Further, we pray not only on our own behalf, but also on the behalf of those souls in purgatory and of those brothers on earth who are in need. Prayer unites us to God; in doing so, we are united to the other members of the Mystical Body.
- http://www.catholic.com/tracts/common-catholic-prayers