Dear Richard:

Sorry for the long delay in answering. (Today in January 22nd) My father was on his death bed during December and died December 25th. I have have been dealing with the estate ever since then and hope to have that concluded this coming week.

The is no excuse for any Catholic to confuse the meaning of the Immaculate Conception with that of the Virgin Birth. But, many Catholics put little effort in knowing their own faith.

The Immaculate Conception is a very important dogma. It is so important that the pope declared the dogma ex cathedra in 1858. This means that the dogma in infallible and that all Catholics are required to believe it or be in a state of heresy.

The Assumption of Mary was also declared ex cathedra in 1953.

The other two doctrines of Mary, the Virgin Birth and her Perpetual Virginity, are in the Bible stated explicitly and implictly, respectively. The Immaculate Conception is also implicitly mentioned in the Bible.

So, we have the following doctrines on Mary:

1) Immaculate Conception
2) Virgin Birth
3) Perpetual Virginity
4) Assumption into Heaven

1) Immaculate Conception: Mary had to be free from original sin. In order for Mary to be the tabernacle of the Christ child, she and her womb had to be pure, undefined, and sanctified (set aside for God).

We learn this economy in the Old Testament by the choice of the lamb of sacrifice. The lamb had to have no blemishes and be a lamb, that is, a pre-sexual (virginal) sheep. Jesus is the lamb of God and thus had to be without blemish and be virginal.

The vessel to which Jesus would enter this world had to be pure and sanctified. The Son of God could not be born of a dirty vessel stained with sin. Thus, Mary had to be preserved from Original Sin, which means that she did not inherent concupiscence (the tendency to sin). This allowed her to be sinless, by her own choice, but a choice that was made easy by the lack of concupiscence and stain of Original Sin. 

Scriptures imply Mary's sinlessness (Immaculate Conception) when the angel called her "full of grace."

2) Virgin Birth: Mary had to be a virgin. We know that Mary did not have sex with her husband, or with anyone else. She was a virgin, yet pregnant by the power of the Holy Spirit. The Scriptures affirm this much. But, her virginity upon the birth of Jesus is also part of the economy I mentioned above.

The tabernacle of God cannot be touched except by sanctified hands. In this case the sanctifier was the Holy Spirit. In addition to the fact that Jesus could not reside in a womb that was stained with sin (hence the Immaculate Conception), we know that the tabernacle of God cannot be touched from the story of the Uzzah who, with good intentions, nevertheless touched and grabbed hold of the the Ark of the Covenant to prevent it from falling off the cart. He was not deputed, or sanctified to touch the Ark. Thus, God stuck him dead.

No one could touch Mary, the Ark of the New Covenant, and live. She as set aside solely for God.

3) Perpetual Virginity: Mary to be perpetually a virgin. Sacred Vessels cannot be used for vulgar (that is, common) purposes. Thus, her womb, which is the Tabernacle of the New Covenant, could not be touched. She had to remain a virgin, as to have sex and bear children would defile the sanctified tabernacle within her.

Think of the tabernacle on your local parish. Now think of that tabernacle being used as a safe to store money in someone's house, or worse, imagine it being used as a bed for a cat.  

The Scriptures affirm that Mary did not have other children. The word translated as "brothers", as in the brothers of our Lord, can also mean cousins, since there was no word for cousins in either Hebrew nor Aramaic. But, the clincher was what Jesus did on the Cross. He gave the care of his mother to John (not a brother or cousin of Jesus). Doing this flies in the face of all Jewish tradition had Jesus brothers. The tradition was that the care of a mother-widow goes to the eldest son. Upon his death, the care goer to the next eldest son. There is no reason for Jesus to slap in the face his brothers, if he had any, by this profound insult. Jesus had no brothers and Mary remained perpetually Virgin.

4) Assumption into Heaven: Mary, as the Ark of the New Covenant, by her Sacred Womb, could not be allowed to die and decay. Sacred things cannot be allowed such a fate. Thus, Mary had to be assumed into Heaven. 

It is interesting that there are no bodily relics of Mary (or Jesus). That is because Mary's body (and our Lord's body) are not found in any grave. Jesus resurrected and ascended into heaven. Mary was assumed into heaven either at the point of death, or just after her death, we are not sure. But, her body was never buried as there was no body to bury,and thus no relics exist and no grave (traditional or actual) exists.

These doctrines are critically important because they shows us the sanctity of Mary, who had to be sanctified in order to carry our Lord in her womb. Thus, this shows us the Jesus is God. These doctrine also show us the nature of the Sacred.

Obviously, the Church considers them important as infallible declarations were made on two of them: Immaculate Conception (also the Scripture implies this) and the Assumption. The Virgin Birth is infallible by its declaration in Scripture. And, the Perpetual Virginity is implied in Scripture and made infallible by the ordinary Magisterium

Resources:

Immaculate Conception and the Assumption

Mary, Full of Grace

Catholic Encyclopedia: Immaculate Conception

St. Thomas Aquinas Summa Theologiae: Immaculate Conception

Catholic Encyclopedia: Assumption

Mary, Ever Virgin

Brethren of the Lord

Catholic Encyclopedia: Perpetual Virginity

Church Fathers: Perpetual Virginity

God Bless,
Bro. Ignatius Mary