Why do we celebrate Mary's birthday?

Answer 1

Roman Catholic AnswerThe Blessed Virgin Mary is the honor of our race. Our Blessed Lord's mother was the "first fruits" of his work of salvation, she is the new Eve who said "yes" to God when Eve said "no". She is the perfect exemplar of holiness, of hope, of obedience, and of union with her son. from The Catechism of the Catholic Church, second edition, English translation 1994

487 What the Catholic faith believes about Mary is based on what it believes about Christ, and what it teaches about Mary illumines in turn its faith in Christ.

We celebrate her birth as that of the first of our race to achieve the perfection that God wants for each one of us, she is the perfect example of what Our Blessed Lord's saving grace can accomplish if we willing let Him.

Answer 2

Because it is the feast of the Immaculate Conception.

Answer 3

She is the mother of God. And also because not only that she is the mother of the Church.

Answer 4

We honor the virgin Mary because she is the Mother of God (Jesus). The Bible itself tells us that all generations shall call her blessed (Luke 1:48).