Why Do Catholics Believe That Mary Was Without Sin? *
The Gospel according to Luke refers to Mary with the Greek word kecharitomene, meaning "highly graced" or "full of grace" (see Lk 1:28). In this deferential term of address used by the angel Gabriel--not used in Scripture of any other human being--we find one indication of an unparalleled grace given by God to our Lady: She was conceived without the defect of original sin. (Catholics call this reality the "Immaculate Conception.") Throughout her life as well, God preserved her from committing any actual sin.
Why would God have granted Mary such a gift? When the eternal Word took on flesh (see Jn 1:14), he took his flesh from her. God wanted his sinless Son, Jesus, to receive his human nature from a sinless mother. And it was most fitting for Jesus to be reared by a woman without sin.
Some Christians have argued that Mary's sinlessness is impossible because St. Paul writes that "all have sinned" (Rom 3:23). But in Scripture the word "all" (pas in Greek) doesn't always mean literally "every single one without exception." For example, in the same letter, St. Paul writes that "all Israel will be saved" (Rom 11:26), yet we suspect that at least some Jewish people will not be saved.
This is also a matter of common Hebrew idiom. In Romans 3:10-12, St. Paul quotes Psalm 14:3, which reads: "All have gone astray; all alike are perverse. Not one does what is right, not even one" (see also Ps 53:2-4). Yet the very next psalm refers to those who walk "without blame" (Ps 15:2). Obviously, then, the lament in Psalm 14:2-3 is emotional and exaggerated language, not intended as a literal utterance. Since St. Paul is referring back to these sorts of passages, the interpretation of his words should take them into account, too.
We should also note that Jesus, who shared our human nature, was without sin (see Heb 4:14-15). This fact alone demonstrates that St. Paul cannot mean that "every single human being has sinned."
Some Christians object that if Mary was sinless, she didn't need Christ as her Savior. But the Church teaches, as does Scripture, that she did indeed need a divine Savior (see Lk 1:47). She wasn't saved out of sin, but rather saved from sin. the rest of us have been delivered out of original and actual sin, while she was preserved from it. Either way, her salvation was God's gracious gift through the merits of her Son.
Other related scriptures: Gn 3:15; Jer 1:5; Lk 1:15.
Catechism of the Catholic Church: 273; 411; 485-495; 508-509; 721-723; 829; 963-972; 2030.
*Quoted from The New Catholic Answer Bible. Wichita, Kansas, Fireside Catholic Publishing, 2005. www.firesidecatholic.com
Additional insights at: www.catholic.com