The Catechism in Questions & Answers

740. What can we derive from the account of creation concerning marriage?

“So God created man in His own image; in the image of God He created him; male and female He created them. Then God blessed them, and God said to them, ‘Be fruitful and multiply; fill the earth and subdue it’” (Genesis 1: 27-28). – Both man and woman are thus created in the image of God. Different yet equal before him, they both stand under the blessing of God.
Human beings are created to have companionship. In their spouses, both man and woman have a counterpart whom they can support and help. “And the Lord God said, ‘It is not good that man should be alone; I will make him a helper comparable to him’” (Genesis 2: 18).
By entering into marriage, man and woman are amalgamated into a single entity intended to last for their lifetime: “Therefore a man shall leave his father and mother and be joined to his wife, and they shall become one flesh” (Genesis 2: 24).