Divine institution

Marriage was instituted by God in the Garden of Eden, when he created Eve and brought her to Adam (Gen 1:27-28; 2:18-24).  Marriage was instituted as the lifelong union of one man and one woman entered into by their mutual consent for the purpose of mutual care, legitimate sexual intercourse, and procreation of children and for avoiding fornication.

Every sexual relationship outside the marriage of one man and one woman instituted by God is sinful. This includes polygamy, homosexuality, fornication, and adultery.

Since marriage is a created order of God known to man also by natural law, the government has no right to change this institution. Same-sex marriage is not to be considered a marriage.

Since marriage is constituted by the mutual consent of the man and the woman, it is not constituted by the state. It is however subject to the fourth commandment so that one should both follow the laws of the land and not marry against the will of one’s parents. When the government has changed the definition of marriage such that it is no longer the lifelong union of one man and one woman, getting a marriage license, in itself, is no longer sufficient to recognize the legitimacy of a marriage.

Procreation

One of the purposes of marriage is procreation of children. Mankind was commanded to be fruitful and to fill the earth (Gen 1:28). Children are a blessing and a gift from the Lord (Ps 127 and 128).

Procreation is therefore not a mere matter of choice. One cannot enter a marriage with the intention of not having children. Birth control therefore is a moral issue and not a mere matter of choice.

We cannot establish a strict rule that prohibits birth control in every situation, where the love of the neighbor may demand it. Nevertheless, birth control should generally be discouraged because children are a gift from God, and one of the primary blessings and fruits of marriage. 

The life of a child starts at conception. Killing a child in its mother’s womb is murder and a sin against the fifth commandment. The same applies to methods of birth control that run the risk of killing children and methods of procreation that create more children than one intends to give birth to.

Divorce

The only legitimate reasons for divorce are adultery (Matt. 19:9) and malicious desertion (1 Cor. 7:15). Malicious desertion includes not only physically abandoning one’s spouse, but also abandoning the marriage by withholding conjugal rights (unless if be for only for a time and by mutual consent, 1 Cor. 7:3–5), and abuse in a form that threatens or endangers the life of one’s spouse or children, thus making it impossible to continue to live together as husband and wife. In such cases, the innocent party may marry again after a legitimate divorce.