Intercessory prayer
Q. Why do Catholics pray to the saints when Jesus is the sole mediator between God and Man?
A. Catholics agree that Jesus is the sole mediator between God and man, but that in no way makes prayer to the saints useless or wrong.
Many times one finds the New Testament recommending intercessory prayer (cf. Col 1:9; 2 Thes 1:11; 2 Thes 3:1; Jas 5:16), and very few Christians seem to have a problem with seeking the prayers of a fellow believer. A difficulty appears to emerge only when that believer has left this earth. But what difference should that make to one who affirms the resurrection of the dead? After all, we read that all are alive in Christ (cf. 1 Cor 15:22).
To recap, then, Jesus Christ is the sole mediator between God and man. No other person in heaven or on earth can take His place. The role of Mary or any other saint is to lead the believer to Christ. This subordinate form of mediation derives its meaning and efficacy from the Lord Himself and is not something the saints possess on their own.
Intercessory prayer is a powerful expression of the beautiful doctrine of the Communion of Saints whereby the saints in heaven, the souls in purgatory, and the faithful on earth are involved and concerned with one another's eternal salvation. Intercessory prayer declares our love for one another in the Church, as well as our faith that the bonds to Christ and His Church forged in baptism cannot be dissolved by death.
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Sole mediator
Q. How can I convince my Fundamentalist friends that Catholics do worship Jesus? They are turned off by our saints and statues, which they think we idolize.
A. As pointed out above, the teaching of the Church is clear: Jesus Christ is the sole mediator between God and man. No other person in heaven or on earth can take His place. The role of Mary or any other saint is to lead the believer to Christ. This subordinate form of mediation derives its meaning and effectiveness from the Lord Himself and is not something the saints possess on their own. Therefore, it is important to distinguish between the adoration owed to the Persons of the Blessed Trinity and the veneration given to the saints.
Similarly, Catholics use medals and statues, but not as talismans or as objects of worship in violation of the First Commandment. Rather, these things are intended to be reminders or aids to devotion which focus one's attention on prayer and the practice of virtue. It would be a rare husband who did not carry in his wallet a photo of his wife and children, not because he worships the photo or his family, but because he loves his family and wishes to have a visual representation of them on his person. Nor have I ever heard a Fundamentalist take offense at the presence of statues of our country's heroes at national monuments. If the heroes of the nation can be so honored, why not the heroes of the Church? Catholics use sacred art in just this way, never fashioning "idols" for false worship.
Prayer to Mary (or to any of the other saints) is not an end in itself but is intended to be a means by which one is led to a deeper union with her Son. Classical spirituality even had a Latin maxim to illustrate the point: Ad Jesum per Mariam ("To Jesus through Mary"). True devotion to Mary never obscures the uniqueness of Christ because Catholics know that the only command of Mary recorded in the Scriptures is one that must be scrupulously obeyed: "Do whatever he [Jesus] tells you" (Jn 2:5).
In the final analysis, devotion to the saints can best be appreciated when one sees the saints in glory as the friends of God and fellow members of the household of faith. If our Fundamentalist friends are to understand this aspect of Catholic spirituality, that is probably the grounds which will make the most sense to them.