What is the purpose of marriage in light of 1 Cor 7?

He who created them from the beginning MADE THEM MALE AND FEMALE, and said FOR THIS REASON A MAN SHALL LEAVE HIS FATHER AND MOTHER AND BE JOINED TO HIS WIFE, AND THE TWO SHALL BECOME ONE FLESH. Matthew 19:4

So what is meant by "the two shall become one flesh?"

Here are my thoughts..

In the old testament the Tabernacle and later, the Temple, was the dwelling place of the essence of God on earth. It was the center of Spiritual life where believers could be closer to their maker. In the new testament our human bodies become The Temple where the Spirit "in dwells." A temple that, in its design puts those created by the human hands of the old testament to shame.

During the act of procreation, the male and female bodies are indeed conjoined as one, but this temporary union always ends with the death of the sperm and egg; unless a new beautiful human life is created. God's purpose for marriage is to bring life, not death.

The new birth, is a human being created by the "union" of the mother & father's unique DNA. "Therefore the two become one." This beautiful and unique union cannot be denied by any one. Not the father, the mother nor the child, no matter how much they may wish is to be so. It cannot be undone nor somehow separated back into it component parts.

Thereby, the reason, or the purpose, for the marriage, that is the child, cannot be undone. Through the legal fiction of divorce, we can pretend the reason no longer exists, but the flesh and bone, the reality of the child, still exists.

But in God's Kingdom, this new birth means much more than a new "human being." When a child is born, don't we believe that an "eternal being" is newly created at that moment? I can understand the science of how my wife and I can create a new human being...But I'm rather confident that I cannot create an eternal being. My wife is amazing. But I doubt even she can create an eternal being.

The birth is a life giving, eternal act of co-creation with our Maker, not a crude, temporary act of procreation between two worldly creatures.

And not only eternal, but an eternal being created in the image of God. And not just in God's image, but ultimately, God asks this "reason for marriage" to become his temple for the in-dwelling of The Holy Spirit. A sanctuary for God's presence on earth. The new place from which Spiritual life on this planet emanates. A place where God gets as close as possible to the heart of the believer.

Just as our ancestors, in the old testament, in faith carefully devoted themselves to build and prepare The Temple with the gifts given to them by God. Today, the mother and father are given the gift of a new life and are asked by God in faith, to carefully devote themselves to prepare this new living Temple for the in-dwelling of the Holy Spirit incarnate.

The Spirit, then becomes that child's Advocate, Counselor, Comforter and Intercessor for the glory of God on this earth and in His heavens. And once having received the sacrament of baptism, may at some point leave their mother and father, be wed to their spouse and be consummated by God to co-create a new eternal temple in God's image.

That is the high purpose and privilege of marriage.

I will add a bit to @Andrew Leach answer.

This is based on JPII's Theology of The Body (http://www.youtube.com/watch?v=2lrZCL4mF1Q)

The role of marriage, is to foreshadow/teach us what the love of the trinity is like and how we are called to participate in it. Love that is fruitful, that created all creation.

Marriage is where man and woman unite in love (total self giving, like that between persons of the trinity) and that love, like the love of the trinity is fruitful. All this, is supposed to show us what is God - fruitful love.

The purpose of marriage is primarily, to help both partners achieve salvation. Procreation, is one of the signs of the love of God. Marriage, cannot be separated from the possibility of procreation, as it would not be a true picture of God and God's love.

Now, as to the passage you quoted, it should be understood in totality of the revelation. It can be understood in many ways, one being that - different people are called to different vocations. In totality of the revelation, I don't think it should be read as condoning release of sexual tension in marriage, or that being the purpose of marriage

Marriage is not, in catholic understanding, a release of passion, or lust. JPII made headlines when he said that EVEN IN MARRAIGE, a man can commit adultery with his wife if his motives are that of lust.

The Catechism of the Catholic Church has

1604 God who created man out of love also calls him to love the fundamental and innate vocation of every human being. For man is created in the image and likeness of God who is himself love.⁹⁰ Since God created him man and woman, their mutual love becomes an image of the absolute and unfailing love with which God loves man. It is good, very good, in the Creator's eyes, and this love which God blesses is intended to be fruitful and to be realized in the common work of watching over creation: "and God blessed them, and God said to them: 'Be fruitful and multiply, and fill the earth and subdue it.'"⁹¹

90 Cf. ⇒ Gen 1:27; ⇒ 1 Jn 4:8, ⇒ 16.
91 ⇒ Gen 1:28; cf. ⇒ 1:31.

The primary reference for this question is Genesis 1:28 with other references, enumerated below.

The Catechism further extols the virtue of marriage with

1613 On the threshold of his public life Jesus performs his first sign — at his mother's request — during a wedding feast.¹⁰⁵ The Church attaches great importance to Jesus' presence at the wedding at Cana. She sees in it the confirmation of the goodness of marriage and the proclamation that thenceforth marriage will be an efficacious sign of Christ's presence.

1616 This is what the Apostle Paul makes clear when he says: "Husbands, love your wives, as Christ loved the church and gave himself up for her, that he might sanctify her," adding at once: "'For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one. This is a great mystery, and I mean in reference to Christ and the Church."¹¹⁰

105 Cf. ⇒ Jn 2:1-11.
110 ⇒ Eph 5:25-26, ⇒ 31-32; Cf. ⇒ Gen 2:24.

Thus marriage is seen as a metaphor for the relationship between Christ and the Church:

It is God's purpose that, as husband and wife give themselves to each other in love throughout their lives, they shall be united in that love as Christ is united with his Church. [Church of England, also CCC1617]

Thus there are two purposes to marriage: to procreate, and to model the relationship between Christ and the Church. Paul's reference to burning with passion might be seen as a desire to become one flesh: to make present that relationship (even if that second purpose might not be exactly uppermost in their mind!) In that case, marry, and demonstrate it.

Gen 1:27 — So God created man in his own image, in the image of God he created him; male and female he created them.

Gen 1:28 — And God blessed them, and God said to them, "Be fruitful and multiply, and fill the earth and subdue it ..."

Gen 1:31 — And God saw everything that he had made, and behold, it was very good.

Gen 2:24 — Therefore a man leaves his father and his mother and cleaves to his wife, and they become one flesh.

Jn 2:1–11 — Wedding at Cana in Galilee

Eph 5:25–26 — Husbands, love your wives, as Christ loved the church and gave himself up for her, that he might sanctify her, having cleansed her by the washing of water with the word.

Eph 5:31–32 — "For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh." This mystery is a profound one, and I am saying that it refers to Christ and the church.

1 Jn 4:8 — He who does not love does not know God; for God is love.

1 Jn 4:16 — ...God is love, and he who abides in love abides in God, and God abides in him.

A lay Catholic interpretation of the Biblical foundation:

The command to procreate is the very first command God gives to mankind that scripture informs us of.

God blessed them and God said to them: Be fertile and multiply; fill the earth and subdue it. Have dominion over the fish of the sea, the birds of the air, and all the living things that crawl on the earth. (Genesis 1:28)

It's reasonable to conclude from a purely Biblical standpoint that, since this command is the first command, it is the most holy and most important command God gives to pre-fallen people. Made in God's image, we are created to create people to share in God's divinity.

That said, it's important not to forget that this command was issued to pre-fallen people. Such people would interpret it not as a call to release sexual tension, but as a call to create people in God's example. Paul, on the other hand, is necessarily speaking to fallen people with a fallen, sinful, tainted understanding of sex, wherein -- as the question illustrates -- they (we) tend to approach intercourse as the mere release of sexual tension.

Paul is therefore (re)declaring sex in quite the opposite manner the question assumes he is. Recognizing sex as the means by which we fulfill God's primal, holy command given to pre-falling people, Paul is attempting to protect its holiness by preventing people from engaging in it flippantly or without the proper recognition of its holiness.