When Catholics pray to Mary and the Saints in Heaven, it is not in worship but in fervent request for their prayers on our behalf. As scripture indicates, those in Heaven are aware of the prayers of those on earth. This can be seen, for example, in Revelation 5:8, where John depicts the Saints in Heaven offering our prayers to God under the form of “golden bowls full of incense, which are the prayers of the Saints”. Those Angels and Saints in Heaven are aware of our petitions and present them to God by interceding for us. It should be noted that asking one person to pray for you in no way violates Christ’s mediatorship between God and man.
St. Paul tells us, first of all, then, I urge that supplications, and thanksgiving be made for all men, all kings and all who are in high positions, that we may lead a quiet and peaceable life, godly and respectful in everyway. This is good, and pleasing to God our Saviour, who desires all men to be saved and to come to the knowledge of the truth (1 Tim2 :1-4).
Intercessory prayers offered by Christians-which is what the saints in Heaven are- on behalf of others is something “good and pleasing to God”,not something infringing on Christ’s role as mediator. Catholics plead the intercession of the Saints because we are informed in the bible that the prayers of certain people are more effective than those of others. “the prayer of a righteous man has great power in its effect”(James 5:16).
Since those who are in heaven been made perfectly righteous and are without sin, their prayers are all the more effective before the throne of God.
FOR MORE ON THIS TOPIC: Catholic Answers, Dave Armstrong, Scripture Catholic.