25.1 MARRIAGE is to be between one man and one woman. It is not lawful for any man to have more than one wife, nor for any woman to have more than one husband, at one and the same time. Gen. 2:24; Mal. 2:15; Matt. 19:5,6.
25.2 God instituted marriage for the mutual help of husband and wife, for the increase of mankind in accordance with His laws, and for the prevention of immorality. Gen. 1:28; 2:18; 1 Cor. 7:2,9.
25.3 It is lawful for all sorts of people to marry, provided that they are able to give their rational consent. But it is the duty of Christians to marry only 'in the Lord'. In consequence, those who profess the Christian faith should not contract marriages with infidels or idolaters. It is also quite unfitting for godly persons to become partners in marriage with persons who lead wicked lives or who maintain damnable heresies. Neh. 13:25-27; 1 Cor. 7:39; 1 Tim. 4:3; Heb. 13:4.
25.4 Marriage must not be contracted within the degrees of blood relationship or kinship forbidden in God's Word. Nor when such incestuous unions occur can they ever be made lawful, either by any law of man or by the consenting parties, and the persons concerned can never rightly live together as man and wife. Lev. 18; Mark 6: 18; 1 Cor. 5: 1.