CATECHISM OF THE CATHOLIC CHURCH
SECOND EDITION

Paragraphs 2397–2401

2397 The covenant which spouses have freely entered into entails faithful love. It imposes on them the obligation to keep their marriage indissoluble.
2398 Fecundity is a good, a gift and an end of marriage. By giving life, spouses participate in God's fatherhood.
2399 The regulation of births represents one of the aspects of responsible fatherhood and motherhood. Legitimate intentions on the part of the spouses do not justify recourse to morally unacceptable means (for example, direct sterilization or contraception).
2400 Adultery, divorce, polygamy, and free union are grave offenses against the dignity of marriage.

You shall not steal.

2401 The seventh commandment forbids unjustly taking or keeping the goods of one's neighbor and wronging him in any way with respect to his goods. It commands justice and charity in the care of earthly goods and the fruits of men's labor. For the sake of the common good, it requires respect for the universal destination of goods and respect for the right to private property. Christian life strives to order this world's goods to God and to fraternal charity.