As an Anglo-Catholic there are few beliefs I hold which irritate other Anglicans and Protestants as much as my belief in the practice of invocing the prayers of the Saints. I would like here to offer a brief defense of the practice and conclude with why I believe it to be an important practice.
There seem to me to be two main objections praying to the saints...
1.) We should only pray to God, through Christ.
2.) The Saints are dead, they cannot hear our prayers.
I would be happy to answer any other objections if a reader thinks I have over-simplified these issues.
The first objection raised usually takes its roots in a verse St. Paul wrote to St. Timothy. "There is one Mediator between God and man, the Man Christ Jesus. (I Tim. 2:5) To this "objection", I would give a hearty "amen". Yes, there is but one Mediator, one go between, for humanity and the Father. The problem with this objection is that it does not stand up as a problem for the doctrine of invoking the prayers of the saints. After all, I would ask anyone I know to pray for me, if I needed prayers for something. That is not undermining the role of Christ as High Priest and Mediator. Rather, it is an acknowledgement that there is a power in corportate prayer. When we ask the saints to pray for us, such as in the Ave Maria, we do not ask the Blessed Mother to go to the Father, but we ask her to pray to her Son; for not even the most glorious of God's creations has access to the Father except through Jesus Christ (John 14:6). Thus, objection #1 fails because the practice does not seek to circumvent Jesus, but to bring more prayers and petitions before him.
The second objection misses some key points. First, the Saints are not dead. Two passages from the Revelation of St. John (6:9-10, 8:3-4) show that the Saints are quite alive and, surprise, surprise, praying! Now, of course, it would be naive to say we have the same level of communication with those who have died as when they were on earth. But as the Scripture plainly teach, there is but one Body of Christ. Therefore, even in death, the Church militant remains united to the Church triumphant. So it is not a stretch to say our communion with the Church on the other side of the vale allows for them to hear us. But I believe this opinion is cemented as fact by the cry of the Martyrs, cited above, from the Revelation. Their question "how long?" until they are vindicated indicates they are more than well aware of what is going on on earth. Aside from this, we have the testimony of Hebrews (12:1) that the saints are a "great cloud of witnesses" surrounding us. As witnesses, they must see and hear what we do. The weight of the evidence suggests that the saints are alive, aware of earthly conditions, and disposed to praying.
Of course, there are not any biblical references of praying TO the deceased. But there does not need to be. There are many things we are not commanded to do, but we do because they are logical and allowable. Furthermore, this practice helps make our prayers more effective. Not necessarily because it means more people are praying (though that does help). St. James teaches us that "the prayer of the righteous man avails much." (James 5:16) Those of us who believe have the righteousness of Christ within us to varying degrees. But the Saints in heaven are fully free from sin. They are more righteous than we are. Therefore, their prayers avail much more than our own.
With all this in mind, I have posted below one of my favorite versions of Ave Maria. This is the Bach/Gounod arrangement performed by Carmen Monarcha.