This is also a good explanation and good read for those interested in understanding where we EO are coming from:
What basis is there for asking the saints to pray for us?
As we have seen, the Church holds in high esteem the memory of exceptionally holy Christians, who during their earthly lives helped many of their fellow believers both physically and spiritually. Therefore, it should be no surprise that she encourages the faithful to seek the continued intercession of such individuals after their passage into the next world. An example of such an appeal is in a hymn to Saint Sergius of Radonezh, a very beloved monk and spiritual father to many in fourteenth-century Russia: "The Holy Spirit took up His abode in thee and operating there adorned thee with beauty. O thou who hast boldness to approach the Holy Trinity, remember thy flock gathered by thy wisdom and never forget it, visiting thy children, according to thy promise, O holy father Sergius".9 A similar appeal is made to Saint Herman, Orthodox evangelizer of Alaska in the early 1800's: "Having one desire, to bring unbelieving people to the One God, thou wert all things to all men: teaching the Holy Scripture and a life in accordance with it, instructing in handicrafts, and being an intercessor before the authorities, nursing men in everything like children, that thus thou mightest bring them to God; and do not leave us who sing to thee".10 Since death has been conquered by Christ, why should not such persons continue their ministry to us after they have joined Christ in heaven? A Russian Orthodox priest in the early twentieth century once chided those who do not believe in a true fellowship of prayer with the departed: "A handful of soil, a tombstone, have become [for you] unconquerable obstacles for communion with those who have departed from the world".11 Countless Christians of all lands and ages have given testimony about receiving help from God through the prayers and ministrations of saints. This is a strong indication that God is well pleased with their prayers for us and ours to them. Scripture attests to the sanctity of such prayers in the Book of Revelation: "The four living creatures and the twenty-four elders fell down before the Lamb, each having a harp, and golden bowls full of incense, which are the prayers of the saints" (Revelation 5:8).
But doesn't the Bible say, "For there is one God and one Mediator between God and men, the Man Christ Jesus" (1 Timothy 2:5)? Why do we need to ask the saints to pray for us?
Yes, Christ Jesus, both Man and God, is the only One who has reconciled fallen humanity to God the Father by His reconciling and redeeming life, death, and resurrection. But this does not mean that we never ask others to pray for us! We ask the departed saints for their prayers in the same way we ask our fellow Christians on earth to intercede for us. Since the departed remain alive in Christ, why should they cease to express their love and concern for us through prayer? Freed from the concerns of day-to-day survival on earth, unencumbered with the sinful tendencies of the flesh, and far more intimately knit together with Christ than we are, the departed are able to intercede for us much more frequently and powerfully than our friends on earth can pray for us. Those in heaven are able to do continuously what we on earth long to do, but usually only manage to do weakly and sporadically. No wonder, then, that Christians from the earliest days have asked the departed for their prayers. This in no way means that we can only reach Christ by going through the saints, as if they are absolutely necessary intermediaries between us and God. Such an idea is completely foreign to Orthodoxy. Saint Paul clearly states, "Seeing then that we have a great High Priest who has passed through the heavens, Jesus the Son of God . . . let us therefore come boldly to the throne of grace, that we may obtain mercy and find grace to help in time of need" (Hebrews 4:14-16). But just because we pray, on our own, directly to God, does not mean that we never ask other people for their prayers! Indeed, we are commanded many times in the Scriptures to pray for one another. Saint Paul says to Timothy, "Therefore I exhort first of all that supplications, prayers, intercessions, and giving of thanks be made for all men" (1 Timothy 2:1; see also Colossians 4:2-4, Ephesians 6:18, etc.). And we are taught by our Lord Jesus that the power of prayer is greater when more people are praying together: "Again I say to you that if two of you agree on earth concerning anything that they ask, it will be done for them by My Father in heaven" (Matthew 18:19). So, just as we feel comforted and strengthened when we ask friends, family, and Church members here on earth to intercede for us in a time of need, how much more can we feel comforted and strengthened when we also ask the Church in heaven for her prayers! (And we should not neglect to ask the angels for their prayers as well, since they are expressly sent to us as "ministering spirits" [Hebrews 1:14; also Psalm 91:11 and Isaiah 63:9]). Asking the saints, both those on earth and those in heaven,12 for their prayers, and asking the angels, too, can all be understood simply as gathering the greatest amount of prayer support possible in a time of need!
Can the saints answer our prayers directly? Is it within their power to grant our requests?
The prayers of our brothers and sisters in Christ here on earth are only effective insofar as God answers them. It is the same with the intercessions of the saints in heaven for us. They can never answer prayers of their own accord or in their own power; they can only beseech Christ on our behalf. To imagine that prayer to the saints means that they can grant our requests apart from Christ is a totally unacceptable idea according to Orthodox theology and practice. So when we pray to the saints, the understanding is always clear that we are asking them to help us by praying to God, and not by their own power or actions apart from Him. For example, a hymn to Saint Nina (who as a young woman in the early fourth century brought the Christian Faith to Georgia, in southern Eurasia) concludes, "with the angels thou hast praised in song the Redeemer, praying constantly for us that Christ may grant us His grace and mercy".13 But as to their ability to hear our requests for their prayers, we ought not to limit the powers of spiritual perception of those who are now so intimately linked with God. If we on earth experience the help of the Holy Spirit praying in us and through us (Romans 8:26, 27), how much more must the Spirit's help be present in the saints in heaven? And we should remember that in heaven, in the spiritual realm, there are none of the limitations of time, space, or physical mortality which so restrict us as we live on earth.
Saints Michael and Gabriel Orthodox Church
But we are all icons of Christ. 
