To understand Catholic marriage in the sacrament of Matrimony, it’s best to begin… …in the beginning.
God didn’t have to make the human race male and female as he did. God didn’t have to share his creative power with his own creatures and make the beginning of a new human life depend upon the free cooperation of a man and a woman with himself. There is a limitless number of other ways in which God could have arranged for the multiplication of human beings, had he chosen to do so.
But God didn’t do it any other way. He chose to make man male and female, and to give him the power, in partnership with himself, to produce new human life. By the act of intimate union which we call sexual intercourse, man and woman would fashion a physical image of themselves; and into this new body so wondrously begun God would infuse a spiritual and immortal soul.