Why did God dispose man and woman for each other?
God disposed man and woman for each other so that they might be "no longer two but one" (Mt 19:6). In this way they are to live in love, be fruitful, and thus become a sign of God himself, who is nothing but overflowing love.
How does the sacrament of Matrimony come about?
The sacrament of Matrimony comes about through a promise made by a man and a woman before God and the Church, which is accepted and confirmed by God and consummated by the bodily union of the couple. Because God himself forms the bond of sacramental marriage, it is binding until the death of one of the partners.
The man and the woman mutually administer the sacrament of Matrimony. The priest or the deacon calls down God's blessing on the couple and, furthermore, witnesses that the marriage comes about under the right circumstances and that the promise is comprehensive and is made publicly. A marriage can come about only if there is marital consent, that is, if the man and the woman enter marriage of their own free will, without fear or coercion, and if they are not prevented from marrying by other natural or ecclesiastical ties (for example, an existing marriage, a vow of celibacy). (YOUCAT questions 260 & 261)
Dig Deeper: CCC section (1601-1605) and other references here.
Part 2: The Celebration of the Christian Mystery (1066 - 1690)
Section 2: The Seven Sacraments of the Church (1210 - 1690)
Chapter 3: The Sacraments at the Service of Communion (1533 - 1666)
Article 7: The Sacrament of Matrimony (1601 - 1666)
"The matrimonial covenant, by which a man and a woman establish between themselves a partnership of the whole of life, is by its nature ordered toward the good of the spouses and the procreation and education of offspring; this covenant between baptized persons has been raised by Christ the Lord to the dignity of a sacrament."84
84.
CIC, can. 1055 § 1; cf. GS 48 § 1.
I. MARRIAGE IN GOD'S PLAN ⇡
Sacred Scripture begins with the creation of man and woman in the image and likeness of God and concludes with a vision of "the wedding-feast of the Lamb."85 Scripture speaks throughout of marriage and its "mystery," its institution and the meaning God has given it, its origin and its end, its various realizations throughout the history of salvation, the difficulties arising from sin and its renewal "in the Lord" in the New Covenant of Christ and the Church.86
85.
Rev 19:7, 9; cf. Gen 1:26-27.
86.
1 Cor 7:39; cf. Eph 5:31-32.
Marriage in the order of creation ⇡
"The intimate community of life and love which constitutes the married state has been established by the Creator and endowed by him with its own proper laws. ... God himself is the author of marriage."87 The vocation to marriage is written in the very nature of man and woman as they came from the hand of the Creator. Marriage is not a purely human institution despite the many variations it may have undergone through the centuries in different cultures, social structures, and spiritual attitudes. These differences should not cause us to forget its common and permanent characteristics. Although the dignity of this institution is not transparent everywhere with the same clarity,88 some sense of the greatness of the matrimonial union exists in all cultures. "The well-being of the individual person and of both human and Christian society is closely bound up with the healthy state of conjugal and family life."89
87.
GS 48 § 1.
88.
Cf. GS 47 § 2.
89.
GS 47 § 1.
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.
Holy Scripture affirms that man and woman were created for one another: "It is not good that the man should be alone."92 The woman, "flesh of his flesh," his equal, his nearest in all things, is given to him by God as a "helpmate"; she thus represents God from whom comes our help.93 "Therefore a man leaves his father and his mother and cleaves to his wife, and they become one flesh."94 The Lord himself shows that this signifies an unbreakable union of their two lives by recalling what the plan of the Creator had been "in the beginning": "So they are no longer two, but one flesh."95
92.
93.
Cf. Gen 2:18-25.
94.
95.