"This truth, showing Jesus' divine origin, was immediately grasped by the first Christians for its important significance and included among the key affirmations of their faith. Son of Joseph according to the law, Jesus in fact, by an extraordinary intervention of the Holy Spirit, was in his humanity only the son of Mary, since he was born without the intervention of man. Mary's virginity thus acquires a unique value and casts new light on the birth of Jesus and on the mystery of his sonship, since the virginal generation is the sign that Jesus has God himself as his Father" (Pope John)

God did not become the Father of Jesus at the virginal conception as this statement implies. He was the begotton Son of God before all things. Did God the Father become the Father of Jesus through Mary? Not in the wildest imagination. That is simply Mormonism. Mormon's believe that when the time was ripe, God the Father knocked at the door of Mary and had an intercourse with her to produce Jesus. Are they right? Certainly the Apost les and the early believers never imagined it. Tha tis not the concept of incarnation.

Bible clearly states that when Jesus was conceived, Mary was a virgin - chaste, who did not know man. This is another way of saying that she never had a sexual intercourse with a man. Why was this necessary? Evidently to maintain that Jesus was fully human and fully God it was necessary that Jesus was born in the Spirit without the intervention of a man. John hints at this idea in

John 1:12 Yet to all who received him, to those who believed in his name, he gave the right to become children of God--
13 children born not of natural descent, nor of human decision or a husband's will, but born of God.

So it was necessary that that Jesus was to be born not of natural descent, nor of human decision, or a husband's will, but born of God.

This birth could have happened by the spirit without a husband's will as a second or a third child in a human family. It was sufficient that Jesus was born of a woman, and born of God without a human father. This satisfies the promise of salvation contained in the curse to Sepent.

Gen. 3:15 And I will put enmity between you and the woman, and between your offspring and hers; he will crush your head, and you will strike his heel."
Is. 7:14 Therefore the Lord himself will give you a sign: The virgin will be with child and will give birth to a son, and will call him Immanuel.

In fact the word used in Isaih for virgin does not mean chaste at all. It simply implies a woman. Yet when the Old Testament cannon was codified about 300 years before Jesus, this verse was considered as a mesianinc prophecy by the Rabis and as a prophecy used the word that meant - virgin.

There are other reasons however why the mesia was to be a first born. I can mention a few.

1. Mesia should be the legal heir to the throne of David. The eldest son in the line usually is the King, according to Jewish tradition. So Jesus was to be legally the first born to Joseph. To be the King of the Jews, he was the first born. He indeed was the legal heir to the throne of David being the first born of Joseph. Joseph' ancestry traced from Davidic Royal line is given in Mathew. The consequence of this is that we cannot consider the "brothers of Jesus" as the children of Joseph from an earlier marriage as is usually emphasized.

2. Mesia was also Priest. He was not to be Levite. He was therefore a Priest by the order of Melchizedek. Every first born of any living belongs to God. Anything that opens the womb belongs to God. So the mesia was to be born as the first born of Mary.

However the major reason for the virgin birth I believe is to make certain that the people believe his birth as truly divine. Hence it was necessary that Mary was to conceive Jesus before Mary and Joseph came together.

However it was not necessary that Mary should remain a virgin. The status of Jesus does not stand or fall on whether Mary remained as a virgin or not. In fact since she was married to Joseph, to keep herself away from her husband would have been a violation of purpose for which male and female were created. It would have been a poor example to the Church and even to the fellow Jews. We should expect her to be a good wife to Joseph. Scripture do indicate clearly that this was so.

Mat. 13:55 "Isn't this the carpenter's son? Isn't his mother's name Mary, and aren't his brothers James, Joseph, Simon and Judas?
56 Aren't all his sisters with us? Where then did this man get all these things?"
The same event is recorded by Mark using almost the same words.

Mark 6:3 Isn't this the carpenter? Isn't this Mary's son and the brother of James, Joseph, Judas and Simon? Aren't his sisters here with us?" And they took offense at him.

If the scripture is to be trusted, Jesus had four brothers and several sisters and as the eldest son plied the profession of his father as a carpenter. In accordance with the Jewish tradition we are given only the names of his borthers - James, Joseph, Simon and Judas and we are not of his sisters..

James became a Leader of the Church soon after his resurrection and Paul specifically refers to him as the brother of Jesus.

Gal 1:19 I saw none of the other apostles--only James, the Lord's brother.

It is true that the word "brother" in Aramaic as in most semitic, oriental and african languages could mean a wider meaning of cousins or even fellow country men. Even in English we call a fellow Christian as a brother.Thus we have these probable meanings for the word brothers here.

(1.) In the natural and common sense (Matt. 1:2; Luke 3:1, 19).
(2.) A near relation, a cousin (Gen. 13:8; 14:16; Matt. 12:46; John 7:3; Acts 1:14; Gal. 1:19).
(3.) Simply a fellow-countryman (Matt. 5:47; Acts 3:22; Heb. 7:5).
(4.) A disciple or follower (Matt. 25:40; Heb. 2:11, 12).
(5.) One of the same faith (Amos 1:9; Acts 9:30; 11:29; 1 Cor. 5:11); whence the early disciples of our Lord were known to each other as brethren.
(6.) A colleague in office (Ezra 3:2; 1 Cor. 1:1; 2 Cor. 1:1).
(7.) A fellow-man (Gen. 9:5; 19:7; Matt. 5:22, 23, 24; 7:5; Heb. 2:17).
(8.) One beloved or closely united with another in affection (2 Sam. 1:26; Acts 6:3; 1 Thess. 5:1).

Brethren of Jesus occurs in these passages Matt. 1:25; 12:46, 50: Mark 3:31, 32; Gal. 1:19; 1 Cor. 9:5. They were probably the younger children of Joseph and Mary. Some have supposed that they may have been the children of Joseph by a former marriage, and others that they were the children of Mary, the Virgin's sister, and wife of Cleophas. The first interpretation, however, is the most natural and most direct.

In Hebrew and Aramaic as in modern Arabic, there are no special words for brother and cousins. In languages that do not have specific terms of cousins, they are usually spelled out clearly when a relation is mentined such as his brother's children etc. However New Testament gospels were not written in Aramaic but in Greek language. In Greek, the word for brother is "adelphos" (plural: adelphoi) and there is a special word for cousin viz. "anepsios". As such in the Old Testament the word for brother has been employed to include the wider family. (1 Sam. 9:13; 20:32; 2 Sam. 1:26; Amos 1:9).But in Greek such a connotation is difficult to establish. At least semantically it is not an interpretation.

However we should note that even in English the word brother is sometimes used to denote anything from a brother to a colleague and they are to be interpreted in the context in which it is spoken . Evidently it is a poor apology to use that explanation to establish ever virginity of Mary.

The Catholic apolegetics refers to the Protoevangelium of James a writing which  date to A.D. 125 for the story of Mary and Joseph.     For a certainity it was not written by James, the brother of Jesus simply because James died much much  earlier. The style and diction of the writing does not justify the authorship at all. There were many such writings of this period as Christianity spread far and wide including the life of Joseph, Life of Jesus in his early childhood etc. with a consequent rise of myths,  legends and heretical teachings and interpretations.  Gnosticism practically invaded Christianity right from the first centuary and dominated during the second centuary.  They were in fact present right at the Apostolic Period. Hence the existence of  Protoevangelium of James and other gospels are not a surprise.  However they do not bear sanctity or tradition because of that.  In fact during beginning of the second centuary several gnostic movements started within the "chritian church", including a strong group who considered Mary as the real goddess.  {Critical analysis of "Protoevangelium of James" the "Pseudo-Matthew" and "the Gospel of the Nativity of Mary" lead to a date of fourth to sixth centuries, and were believed by the sects found in Arabia. The backdrop of these stories are essentially Arab in nature and not Jewish}
It was process of substitution of Mary in place of their own pagan goddess.  A detailed treatment of this and its lingering effect in Roman Art can be found in the Mary myths. The deification attempts of Mary had brought forth similar movements in India and the US. I have just seen a sticker on a car which says: "My Goddess gave birth to your God." A Hindu could really say that because the firs tappearance of Brahman in a form was as a woman "Kaamakshi" who is the mother of all creation. This identification is easy for most Hindus. Hence we notice that the greatest demand for deification of Mary is from India. Is there any wonder?

One problem with the Mary's presence in the Temple as a maid is that no such practice existed in Israel's history. In fact young virgins were permanent part of the Greek, Roman and Arabian pagan temples. They were called virgins but were actually similar to the Devadasis of Indian temples. They were temple prostitutes. They were advised not to become pregnant during their service period, for their own sake. However if they did, their children were considered as Sons of god. In fact all virgins were supposed to do the temple duty before their marriages in certain Greek and Roman area. (This was their sex education). The implication here is certainly serious and I suppose not worth discussing. We are certainly not talking of a Mary who was a temple prostitute. I am mentioning it here because this is the aproach made by the Gnostic sections even today. In that process some give the credit of being the father of Jesus to a Roman Soldier and others to Zachariah, the priest to whom Mary went immediately after hearing the words of Gabriel.

On interesting point to note is that Luke, who was essentially a historian, who did extensive research before he wrote down the account of Jesus, who cared enough to give details of the birth of John the Baptist do not even mention anything about the history of Mary.

Essentially what we are trying to say is on the basis of available historical and scriptural evidence we cannot establish that Mary was an eternal virgin. It is probable and certainly possible but certainly not necessary.  But then Roman Catholic Church being the "custodian of faith and revelation" has stipulated it. As in most of the later Marain doctrines, this doctrineof eternal virginity of Mary is derived from an ardent idolatorous approach to the figure of Mary and the lingering blasphemy of Gnosticism within the Chruch. It is not corroborated by the scripture nor are they ever referred to by any of the Apostles or anyone of the early Church Fathers before the second centuary. The important point is that such a position is not necessary for any christian doctrine.