Only God hears prayers. He hears and intercedes on behalf of his own and for his glory.
1 Tim 2:1-2 - because Jesus Christ is the one mediator between God and man (1 Tim. 2:5), many Protestants deny the Catholic belief that the saints on earth and in heaven can mediate on our behalf. But before Paul's teaching about Jesus as the "one mediator," Paul urges supplications, prayers, intercessions, and thanksgivings be made for all people. Paul is thus appealing for mediation from others besides Christ, the one mediator. Why?
1 Tim 2:3 - because this subordinate mediation is good and acceptable to God our Savior. Because God is our Father and we are His children, God invites us to participate in Christ's role as mediator.
1 Tim. 2:5 - therefore, although Jesus Christ is the sole mediator between God and man, there are many intercessors (subordinate mediators).
1 Cor. 3:9 - God invites us to participate in Christ's work because we are God's "fellow workers" and one family in the body of Christ. God wants His children to participate. The phrase used to describe "fellow workers" is "sunergoi," which literally means synergists, or cooperators with God in salvific matters. Does God need fellow workers? Of course not, but this shows how much He, as Father, loves His children. God wants us to work with Him.
Mark 16:20 - this is another example of how the Lord "worked with them" ("sunergountos"). God cooperates with us. Out of His eternal love, He invites our participation.
Rom. 8:28 - God "works for good with" (the Greek is "sunergei eis agathon") those who love Him. We work as subordinate mediators.
2 Cor. 6:1 - "working together" (the Greek is "sunergountes") with him, don't accept His grace in vain. God allows us to participate in His work, not because He needs our help, but because He loves us and wants to exalt us in His Son. It is like the father who lets his child join him in carrying the groceries in the house. The father does not need help, but he invites the child to assist to raise up the child in dignity and love.
Heb. 12:1 - the cloud of witnesses (nephos marturon) that we are surrounded by is a great amphitheatre of witnesses to the earthly race, and they actively participate and cheer us (the runners) on, in our race to salvation.
1 Peter 2:5 - we are a holy priesthood, instructed to offer spiritual sacrifices to God. We are therefore subordinate priests to the Head Priest, but we are still priests who participate in Christ's work of redemption.
Rev. 1:6, 5:10 - Jesus made us a kingdom of priests for God. Priests intercede through Christ on behalf of God's people.
James 5:16; Proverbs 15:8, 29 - the prayers of the righteous (the saints) have powerful effects. This is why we ask for their prayers. How much more powerful are the saints prayers in heaven, in whom righteousness has been perfected.
1 Tim 2:5-6 - therefore, it is because Jesus Christ is the one mediator before God that we can be subordinate mediators. Jesus is the reason. The Catholic position thus gives Jesus the most glory. He does it all but loves us so much He desires our participation.