The Bible tells that those in heaven are praying for us (Rev. 5:8). The Bible also tells us that our brothers and sisters in heaven surround us as a “great cloud of witnesses” (Hebrews 12). And these “witnesses who have preceded us into the kingdom, especially those whom the Church recognizes as saints, share in the living tradition of prayer by the example of their lives, the transmission of their writings, and their prayer today. They contemplate God, praise him and constantly care for those whom they have left on earth. When they entered into the joy of their Master, they were “put in charge of many things.” Their intercession is their most exalted service to God’s plan. We can and should ask them to intercede for us and for the whole world.” *Catechism of the Catholic Church * 2683. How “precious in the sight of the Lord is the death of His saints” (ps. cxvi.15).
No one prays to dead saints, because those who are in heaven are more alive than we are. The Lord is God of the living, not of the dead. In the 5th century the intercession of the saints is mentioned in the Constitutions of the Holy Apostles Book VI: "The souls of the righteous are in the hands of God."For those that have believed in God, although they are asleep, are not dead. For our Saviour says to the Sadducees: "But concerning the resurrection of the dead, have ye not read that which is written, I am the God of Abraham, and the God of Isaac, and the God of Jacob? God, therefore, is not the God of the dead, but of the living; for all live to Him.“
“We pray to Mary for her intercession as our mother. Mary is the perfect Orans (pray-er), a figure of the Church. When we pray to her, we are adhering with her to the plan of the Father, who sends his Son to save all men. Like the beloved disciple we welcome Jesus’ mother into our homes, for she has become the mother of all the living. We can pray with and to her. The prayer of the Church is sustained by the prayer of Mary and united with it in hope.” Catechism 2679 Prayer between members of the body of Christ is indeed pleasing to the Lord, who is the one mediator (1 Tim 2:1-5).
Prayer to the saints simplified: 1) The fervent prayer of a righteous man is very powerful (James 5:16). 2) Those in heaven are surely righteous, since nothing unclean can enter heaven (Rev. 21:27). 3) Those in heaven are part of the mystical body of Christ, and have not been separated from us by death, but surround us as a great cloud of witnessess (Hebrews 12:1). 4) They stand before the throne of God and offer our prayers to Him (Revelation 5:8), and cheer us on as we run the good race. Intercession between members of the body of Christ is pleasing to God (1 Timothy 2:1-4), and even commanded by Him (John 15:17).