Scripture doesn’t say Mary was. It says she was “favored”. It does say Stephen was “ full of grace” but not sinless.
The angel Gabriel said, “Hail, full of grace, the Lord is with you” (Luke 1:28). The phrase “full of grace” is a translation of the Greek word kecharitomene. It therefore expresses a characteristic quality of Mary.
The traditional translation, “full of grace,” is better than the one found in many RECENT versions of the New Testament, which give something along the lines of “highly favored daughter.” Mary was indeed a highly favored daughter of God, but the Greek implies more than that (and it never mentions the word for “daughter”). The grace given to Mary is at once permanent and of a unique kind.Kecharitomene is a perfect passive participle of charitoo, meaning “to fill or endow with grace.” Since this term is in the perfect tense, it indicates that Mary was graced in the past but with continuing effects in the present. So, the grace Mary enjoyed was not a result of the angel’s visit. In fact, Catholics hold, it extended over the whole of her life, from conception onward. She was in a state of sanctifying grace from the first moment of her existence.
She, herself exclaims that Christ is her Savior. In the Scripture we read that “all have sinned” (Rom. 3:23). Besides, they say, Mary said her “spirit rejoices in God my Savior” (Luke 1:47), and only a sinner needs a Savior.
Let’s take the second citation first. Mary, too, required a Savior. Like all other descendants of Adam, she was subject to the necessity of contracting original sin. But by a special intervention of God, undertaken at the instant she was conceived, she was preserved from the stain of original sin and its consequences. She was therefore redeemed by the grace of Christ, but in a special way—by anticipation.
Remember that “nothing is impossible for God.”
Consider an analogy: Suppose a man falls into a deep pit, and someone reaches down to pull him out. The man has been “saved” from the pit. Now imagine a woman walking along, and she too is about to topple into the pit, but at the very moment that she is to fall in, someone holds her back and prevents her. She too has been saved from the pit, but in an even better way: She was not simply taken out of the pit, she was prevented from getting stained by the mud in the first place. This is the illustration Christians have used for a thousand years to explain how Mary was saved by Christ. By receiving Christ’s grace at her conception, she had his grace applied to her before she was able to become mired in original sin and its stain.