I think the OP has to remember that as Catholics we believe that we are
truly called to be sons of God. It took a while for me, as a former Protestant myself, to fully realize the implications of this very Biblical teaching. Scripture clearly teaches that Our Lord is the one mediator between man and God - yet at the same time, we see examples of others (as other posters have already illustrated) both on earth and in heaven (eg. the elders in Revelation 4 and the angel in Revelation 8 both offering up intercessory prayers in heaven) participating in Our Lord’s work of mediation. Why is this? Is Our Lord’s intercession insufficient? Was His work on the cross insufficient? Not at all! The simple answer is, simply put, that Our Lord WILLS to share His divine work with his adopted brothers and sisters…and most especially with His Holy Mother through whom He adopted our own human nature. The Church teaches that Second Person of the Blessed Trinity assumed our lowly human nature in order to glorify it and raise it to eternal glory. In the person of Jesus, mankind has conquered death and reigns in glory at the right hand of the Father. John 1:12 tells us that Christ gave those whom He called the
power to become sons of God…when we are adopted as sons and daughters of God at our baptism, we aren’t simply given a cool title…we are truly
transformed, through the sacraments, in our very being, truly participating in the divine sonship of Christ. St. Paul teaches us that we are destined to share in Christ’s glory as his co-heirs (Romans 8:17). This is not something that we deserve nor something that we can merit…it is a gift of infinite value that Christ the Man-God won for his adopted brothers and sisters, the human race, through his passion, death, and resurrection. If we are co-heirs of Christ, how can you logically deny that we, especially those who have been perfected in heaven, the saints and Our Blessed Mother, can also be his co-intercessors? Especially when we are commanded again and again to intercede for one another in Scripture. Our Blessed Lady, through whom Our Lord affected the mystery of the Incarnation, plays a special role in salvation and, as His most holy and perfect mother, is closest to His Sacred Heart…we can already see in Scripture at the wedding of Cana that her role is to intercede for her children - not because Christ’s intercession is insufficient, but because He
wills to share His glory with his saints - particularly with His Mother. If you read the account of Cana in John 2, Our Lord clearly tells His Mother that it was
not his time…so why did He perform the miracle if it was not yet His time? The answer is obvious - out of His love for Her, as the perfect Mother he himself created to make possible our salvation, He will not deny her requests.
Catechism of the Catholic Church #460:
I would invite the OP to also meditate on the Scripture verses/comments here
scripturecatholic.com/blessed_virgin_mary.html and here
scripturecatholic.com/saints.html