The historic Christian practice of asking our departed brothers and sisters in Christ—the saints—for their intercession has come under attack in the last few hundred years. Though the practice dates to the earliest days of Christianity and is shared by Catholics, Eastern Orthodox, the other Eastern Christians, and even some Anglicans—meaning that all-told it is shared by more than three quarters of the Christians on earth—it still comes under heavy attack from many within the Protestant movement that started in the sixteenth century.
Can They Hear Us?
One charge made against it is that the saints in heaven cannot even hear our prayers, making it useless to ask for their intercession. However, this is not true. As Scripture indicates, those in heaven are aware of the prayers of those on earth. This can be seen, for example, in Revelation 5:8, where John depicts the saints in heaven offering our prayers to God under the form of "golden bowls full of incense, which are the prayers of the saints." But if the saints in heaven are offering our prayers to God, then they must be aware of our prayers. They are aware of our petitions and present them to God by interceding for us.
Some might try to argue that in this passage the prayers being offered were not addressed to the saints in heaven, but directly to God. Yet this argument would only strengthen the fact that those in heaven can hear our prayers, for then the saints would be aware of our prayers even when they are not directed to them!
In any event, it is clear from Revelation 5:8 that the saints in heaven do actively intercede for us. We are explicitly told by John that the incense they offer to God are the prayers of the saints. Prayers are not physical things and cannot be physically offered to God. Thus the saints in heaven are offering our prayers to God mentally. In other words, they are interceding.
The Bible directs us to invoke those in heaven and ask them to pray with us. Thus in Psalms 103, we pray, "Bless the Lord, O you his angels, you mighty ones who do his word, hearkening to the voice of his word! Bless the Lord, all his hosts, his ministers that do his will!" (Ps. 103:20-21). And in Psalms 148 we pray, "Praise the Lord! Praise the Lord from the heavens, praise him in the heights! Praise him, all his angels, praise him, all his host!" (Ps. 148:1-2).
Not only do those in heaven pray with us, they also pray for us. In the book of Revelation, we read: "[An] angel came and stood at the altar [in heaven] with a golden censer; and he was given much incense to mingle with the prayers of all the saints upon the golden altar before the throne; and the smoke of the incense rose with the prayers of the saints from the hand of the angel before God" (Rev. 8:3-4).
And those in heaven who offer to God our prayers aren’t just angels, but humans as well. John sees that "the twenty-four elders [the leaders of the people of God in heaven] fell down before the Lamb, each holding a harp, and with golden bowls full of incense, which are the prayers of the saints" (Rev. 5:8). The simple fact is, as this passage shows: The saints in heaven offer to God the prayers of the saints on earth.
You can read more here if you are truly interested.
http://www.catholic.com/library/praying_to_the_saints.asp