This is an excerpt from a letter that a fellow apologist wrote to his aunt. It is here reprinted with his permission. If you have any questions about what is written here, you can e-mail him - his name is Carl.
There is further Biblical evidence for this belief. It is found in Luke 1:28 and the angel’s greeting to Mary: "And coming in, he said to her, "Hail, favored one! The Lord is with you." The translation "favored one" is flawed and reflects a Protestant bias. The Greek word is kecharitomene and the root word (underlined) is "charis" from which the words "charity" or "grace" comes. In fact, everywhere else in the New Testament this word is translated "grace" as it should be (for example, John 1:14 & 17, in referring to Jesus being full of "grace and truth").
Luke 1:28 literally reads, "Hail, Full of Grace! The Lord is with you." There are a couple of things to note in this short sentence:
1. "Hail" was a greeting of profound respect, usually used for royalty. It was accompanied by a gesture of obeisance. For an angel to say anything like this to a mere mortal is unique in the Bible. Here the angel acknowledges a creature greater than himself, while in the rest of Scripture it is always the humans who acknowledge the greatness of the angels (i.e. Isaiah 1).
2. "Full of Grace" is both a title and a description. The greeting is like that given to royalty. And it means Mary was graced by God, being conceived without sin and always choosing God’s grace over evil. In Catholic doctrine, grace is the life of God given to men, not merely an external favor towards men. Thus salvation comes when we have faith in Christ and God infuses us with grace, his divine life, by the work of his Son and the power of the Holy Spirit. Original Sin is an absence of grace. To be full of grace would require the absence of Original Sin and also the stains of that Sin, which is the inclination towards wrong acts. This grace was given to Mary when she was conceived, preserving her from sin.
It may helpful to consider the words of Paul to the believers at Ephesus: Blessed be the God and Father of our Lord Jesus Christ, who has blessed us with every spiritual blessing in the heavenly places in Christ, just as He chose us in Him before the foundation of the world, that we should be holy and blameless before Him. In love He predestined us to adoption as sons through Jesus Christ to Himself, according to the kind intention of His will, to the praise of the glory of His grace, which He freely bestowed on us in the Beloved" (Eph. 1:3-6).
If God knew us before the foundation of the world, wouldn’t he have also intimately known the woman he would ask to bring the God-man into the world? Wouldn’t the Son, before time and creation, have considered who was to be his mother and have chosen to honor her in a way only he could? And would he have asked a woman with sin, who lacked the fullness of his life, to bring him into the world as Incarnate God?
Grace is absolutely necessary to a relationship with God because he recognizes his own Trinitarian life in us and thus has communion with us. And the bridge between our fallen humanity and this grace is the God-man, Jesus Christ, who was perfect humanity and completely God, who came into history and time through the sinless, but completely mortal, person of Mary.