Why do Catholics believe Mary was sinless?

Answer 1

Because Mary vowed herself to it.

St. Anne (Mary's mother) vowed that her child would be devoted to the service of the Lord. The Jewish custom was that all women who served at the temple of the Lord were to be perpetual virgins. They were forbidden from a normal child-rearing life. So even though she eventually was conceived by the Holy Spirit, she still was bound by her vows.

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Answer 2

The Catholic Church teaches that Mary remained a virgin even after the birth of Jesus.

Roman Catholic AnswerThe Church teaches the perpetual virginity of the Blessed Virgin Mary because it is true, it a great grace and favor from God, and it has always been taught and believed, it is a dogma of faith that has been infallibly taught, as well:

The Perpetual virginity of Mary

Pope Paul IV, in his Constitution, Cum Quorumdam Hominum, of 1555, expressed the constant teaching of the Catholic Church concerning both the virgin birth of Jesus Christ and the perpetual virginity of Mary:

We question and admonish all those who . . . have asserted, taught, and believed . . . that our Lord . . . was not conceived from the Holy Spirit according to the flesh in the womb of the Blessed Mary ever Virgin, but, as other men, from the see of Joseph . . . or that the same Blessed Virgin Mary is not truly the mother of God and did not retrain her virginity intact before the birth, in the birth, and perpetually after the birth. (In Neuner and Dupuis, The Christian Faith, 217. See CCC, pars 484-486, 496-498, 502-506, 510, 723 (for the virgin birth); pars 499-501, 507, 510, 721 (for the perpetual virginity of Mary))

The Greek word for brother in the New Testament is adelphos. The well-known Protestant linguistic reference An Expository Dictionary of the New Testament Words defines it as follows:

1. Male children of the same parents . . .

2. Male descendants of the same parents, Acts 7:23, 26; Hebrews 7:5 . . .

4. People of the same nationality, Acts 3:17, 22; Romans 9:3 . . .

5. Any man, a neighbor, Luke 10:29; Matthew 5:22, 7:3;

6. Persons united by a common interest, Matthew 5:47;

7. Persons united by a common calling, Revelation 22:9;

8. Mankind, Matthew 25:40; Hebrews 2:17;

9. The disciples, and so, by implication, all believers, Matthew 28:10; John 20:17;

10. Believers, apart from sex, Matthew 23:8; Acts 1:15; romans 1:13; 1 Thessalonians 1:4; Revelation 19:10 (the word sisters is used of believers, only in 1 Timothy 5:2) . . . . (Vine, An Expository Dictionary of New testament Words, Vol. 1, 154-155.)

It Is evident, therefore, from the range of possible definitions of adelphos, that Jesus' "brothers" need not necessarily be siblings of Jesus on linguistic grounds, as many commentators, learned and unlearned, seem to assume uncritically. Be examining the use of adelphos and related words in Hebrew, and by comparing Scripture with Scripture ("exegesis"), one can determine that most sensible explanation of all the biblical date taken collectively. Many examples prove that adelphos has a very wide variety of meanings:

In the King James Version, Jacob is called the "brother" of his Uncle Laban (Gen. 29:15; 29:10). The same thing occurs with regard to Lot and Abraham (Gen. 14:14; 11:26-27). The Revised Standard Version uses "kinsman" at 29:15 and 14:14.

Use of brother or brethren for mere kinsmen: Deuteronomy 23:7; 2 Samuel 1:26; 1 Kings 9:14, 20:32; 2 Kings 10:13-14; Jeremiah 24:9; Amos 1:9).

In Luke 2:41-51, ... it is fairly obvious that Jesus is the only child....

Jesus himself uses brethren in the larger sense: Matthew 23:8, 23:1; 12:49-50.

The term Firstborn means pre-eminent and nowhere assumes later siblings, etc.

Answer 3

Roman Catholic AnswerCatholics believe that Mary was sinless from the first moment of her conception, in other words, she was free from the taint of original sin. This is due solely due a gift of God due to the fact that she was to bear His Son, whom no evil could touch. We call this the Immaculate Conception and it was solemnly defined by Pope Pius IX in 1864, although the Church has always believed this. It is called an implicit doctrine, in other words it is not spelled out until the nineteenth century, but follows from other doctrines. Bottom line, it was revealed by God.

from Modern Catholic Dictionary by John A. Hardon, S.J. Doubleday & Co., Inc. Garden City, NY 1980

Immaculate Conception. Title of the Blessed Virgin as sinless from her first moment of existence. In the words of Pope Pius IX's solemn definition, made in 1864, "The most holy Virgin Mary was, in the first moment of her conception, by a unique gift of grace and privilege of almighty God, in view of the merits of Jesus Christ the Redeemer of mankind, preserved free from all stain of original sin." This means that since the first moment of her human existence the mother of Jesus was preserved from the common defect of estrangement from God, which humanity in general inherits from the sin of Adam. Her freedom from sin was an unmerited gift of God or special grace, and an exception to the law, or privilege, which no other created person has received.