1. Marriage is to be between one man and one woman: neither is it lawful for any man to have more than one wife, nor for any woman to have more than one husband, at the same time (Gen. 2:24; Matt. 19:5–6; Prov. 2:17).
One man, one woman, one time. Polygamy is excluded because it is not in keeping with God's creation design for man and woman. God created Adam and one woman, not Adam and three women. Christ is the bridegroom of the church, and Christ provides the ultimate example of monogamy. The elders of the Christian church are required to be monogamous, thus reflecting this ultimate pattern. The Old Testament examples of polygamy are not to be categorized as sinful in the same way that adultery is, but it did definitely fall short of the creation pattern, and thus is unlawful in Christian cultures. Polyandry is excluded in the very nature of things. A husband is the head of his wife, and if a wife has two husbands, she is placed in an impossible governmental situation. A man cannot serve two masters, and neither can a woman.
2. Marriage was ordained for the mutual help of husband and wife (Gen. 2:18), for the increase of mankind with a legitimate issue, and of the Church with an holy seed (Mal. 2:15); and for preventing of uncleanness ( 1 Cor. 7:2, 9).
Why is marriage? First, the husband and wife are created to provide godly help to one another—companionship in the fullest sense of that word. Secondly, God knew that Adam was unable to populate the world by himself, and so He gave him the woman. The purpose of our being constituted male and female is the propagation of godly offspring. And, thirdly, marriage is ordained for the sake of the marriage bed, which in a fallen world is a great help in the prevention of various forms of sexual immorality.
3. It is lawful for all sorts of people to marry, who are able with judgment to give their consent (Heb. 13:4; 1 Tim. 4:3; 1 Cor. 7:36–38; Gen. 24:57–58). Yet is it the duty of Christians to marry only in the Lord (1 Cor. 7:39). And therefore such as profess the true reformed religion should not marry with infidels, papists, or other idolaters: neither should such as are godly be unequally yoked, by marrying with such as are notoriously wicked in their life, or maintain damnable heresies (Gen. 34:14; Exod. 34:16; Deut. 7:3–4; 1 Ki. 11:4; Neh. 13:25–27; Mal. 2:11–12; 2 Cor. 6:14).
Just as God gave permission to eat from any of the trees in the Garden of Eden, so men and women may marry as they please, and marry whom they please. One important restriction must be remembered—Christians must only marry Christians. In the first place, this means that those who profess the true reformed religion may not marry those who are overtly outside the pale, such as atheists, papists, or idolaters in other respects. But it is also possible for individuals to profess the true religion, but to live in a wicked way, or to profess heretical opinions. The fact that they externally belong to the same church as a true believer does not make them a lawful candidate for marriage.
4. Marriage ought not to be within the degrees of consanguinity or affinity forbidden by the Word (Lev. 18; 1 Cor. 5:1; Amos 2:7). Nor can such incestuous marriages ever be made lawful by any law of man or consent of parties, so as those persons may live together as man and wife (Mark 6:18; Lev. 18:24–28). The man may not marry any of his wife’s kindred, nearer in blood than he may of his own: nor the woman of her husband’s kindred, nearer in blood than of her own (Lev. 20:19–21).
The Old Testament restrictions on marriage continue. A man may not marry his sister, for example. The important thing to note here is that the law of man, or agreement of parties, cannot make such a union into a marriage. In such an instance, we would have to speak of "marriage," just as we do with homosexual "marriages." A brother and sister who got "married," assuming it to have been legal, should, upon repentance, separate and divorce. This would not be the requirement, for example, of someone who married unlawfully in another way (e.g. unlawfully divorced before the marriage). In that situation, repentance would not result in a divorce. The section in bold was dropped by the Presbyterian Church in the United States in 1886, and is not in the PCA version of the Confession, which is a good thing. The restriction there goes beyond the boundaries of Scripture, and, in a certain measure, against Scripture.
5. Adultery or fornication committed after a contract, being detected before marriage, giveth just occasion to the innocent party to dissolve that contract (Matt. 1:18–20). In the case of adultery after marriage, it is lawful for the innocent party to sue out a divorce (Matt. 5:31–32): and, after the divorce, to marry another, as if the offending party were dead (Matt. 19:9; Rom. 7:2–3).
An engagement may be broken if there is infidelity on the part of the other person after the engagement is made. Although the Confession does not address the question, an engagement may also be broken if there was earlier hidden immorality.
Say, for example, that a woman represented herself as a virgin although she was not. If the man enters into the betrothal believing this to be the case, when he discovers the truth, he may break the engagement (or marriage). In the case of adultery, the innocent person may divorce the other, and is completely free from the law of marriage in every respect. It is as though the offending party had died, because behavior has consequences.
6. Although the corruption of man be such as is apt to study arguments unduly to put asunder those whom God hath joined together in marriage: yet, nothing but adultery, or such willful desertion as can no way be remedied by the Church, or civil magistrate, is cause sufficient of dissolving the bond of marriage (Matt. 19:8–9; 1 Cor. 7:15; Matt. 19:6): wherein, a public and orderly course of proceeding is to be observed; and the persons concerned in it not left to their own wills, and discretion, in their own case (Deut. 24:1–4).
Men like to "study arguments" that might be able to get them into bed with other women. The fact that the Bible allows for divorce under certain conditions should not be used to justify this approach to justified lust. But only two conditions may set a person free to marry another. The first is adultery, and has already been addressed. The second is willful desertion that is beyond ecclesiastical or civil remedy. And when the conditions are met, the obtaining of a divorce should be a big deal, with a judicial and open approach being taken, and the aggrieved person not left to adjudicate their own case. In a corrupt time, as ours is, the civil and ecclesiastical authorities will frequently refuse to do their duty. In such a case, the innocent person may have to make their own decisions, but this is not the way it ought to be.