Frist, we believe that prayers help. It is customary to ask fellow Christians to pray for us or to pray for others. That would be ntercessionary prayer. We do it all the time.
Second, Christians believe that those who die are not dead but alive in an intermediate state between particular and final judgment. If they are alive, they can pray.
Third, if they prayed when they were on earth, we have very reason to believe that they pray as we speak/write.
Fourth, saints are Christian heroes that we hold in high regard and many of us use one particular saint to fashion our life in faith around theirs.
Fifth, intercessionary prayers to the saints and angels are just that: asking those who pray to pray for us in heaven as we ask others to pray for us on earth.
Intercessionary prayer is a perfectly orthodox practice, rooted in the most fundamental Christian truths.
Only confused Protestants can see "idolatry" in intercesisonal prayers. We do not worship saints and angels. We worship only God. We ask all Christian, on earth as in heaven, to pray for us, and that's not worship.
That is fine if that is the Catholic position, but scripture does not appear to support it:
2 Cor. 5:6-8 : "6 Therefore we are always confident and know that as long as we are at home in the body we are away from the Lord. 7 We live by faith, not by sight. 8 We are confident, I say, and would prefer to be away from the body and at home with the Lord."
As a status in either case, being "in the body and away from the Lord" is directly compared to being "out of the body and with the Lord". This leads directly away from any kind of waiting period idea.
Fifth, intercessionary prayers to the saints and angels are just that: asking those who pray to pray for us in heaven as we ask others to pray for us on earth.
I suppose that I have just never understood the need for this. I agree that God wants us to pray for others on earth, and that it is right and proper to ask someone here to pray for us. We are certain that it happens from personal experience. But to believe that there are saints and angels up there waiting for us to beseech them requires going outside of Biblical teaching. Why not just pray to God? Isn't a function of the Spirit to help you do just that? Do saints and angels have greater "pull" with God? Isn't every minute spent praying to a saint or angel a minute spent not praying to God?