Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel.
I also believe Mary was favored by God for this purpose. She was also of the lineage of David and that made Jesus true heir to the throne. She was pure and faithful. I do not believe, nor does Scripture teach, that she was sinless nor that she herself was immaculately conceived.
This does not demean her or Jesus Christ. It is stating what we know from the Word of God and what he has revealed to us. You MUST believe what your magesterium teaches even if it is man's conjecture or the arrived at agreement to arguments among religious scholars. You are not allowed to question or believe anything contrary to their teachings under fear of excommunication.
What does belief in Mary's perpetual virginity, her own sinless conception by her mother and her “direct line” to her son Jesus as a “Jewish mother” have to do with your salvation? Is it germane to the doctrine that we are saved by grace through faith in Jesus Christ? Does non-belief in those certain doctrines effect in any way the accepting of the free gift of eternal life? They are not. They are not major issues except to those that read more into the plan of salvation.
These doctrines tells us more about Jesus than about Mary. The great question of the Bible is Who is Jesus. The Marian doctrines tell us he is God. The history of the Reformation tell us that if we abandon these doctrines, there is immediately a turn away from the doctrine of the Trinity and a refusal to accept the full divinity of Christ, to something like Arianism. Calvin’s great “sin” —in the eyes of liberals—is his execution of a man who preached this.