Marriage in the Old Testament (in Encyclopedia of Catholic Doctrine, Our Sunday Visitor, 1997. Ed: Russell Shaw)
The book of Genesis contains two accounts of the creation of the sexes and the institution of marriage. "God created man in his own image...; male and female he created them. And God blessed them, and God said to them, 'Be fruitful and multiply'" (Gn 1:27-28). "Then the Lord God said, 'It is not good that the man should be alone: I will make him a helper fit for him'... [and God made woman]. Then the man said, 'This at last is bone of my bones and flesh of my flesh'... Therefore a man leaves his father and his mother and cleaves to his wife, and they become one flesh" (Gn 2:18-24).
In these texts, the basic equality of the sexes appears, along with their complementary roles. The two institutional ends of marriage - procreation and the good of the spouses - are also indicated. The expression "the two become one flesh" presupposes a singular and inseparable union, the marriage bond being therefore exclusive by nature (one man with one woman) and breakable only by death.
Although the Chosen People of the Old Testament received this revelation about the nature of marriage, they did not always observe it in practice. Procreation was given such importance that a man was allowed to have several wives. Moreover, divorce was allowed in certain instances. Jesus, against all the currents of his times, rejected divorce as contrary to the divine plan ("from the beginning it was not so": Mt 19:8); and insisted on the uniqueness of the marriage covenant, where "two" become an inseparable "one": "Have you not read that he who made 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'? So they are no longer two but one. What therefore God has joined together, let no man put asunder" (Mt 19:4-6).