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, Mal.2.15, Matt 19.5-Matt 19.6
Marriage was ordained for the mutual help of husband and wife, for the increase of mankind with a legitimate issue, and the preventing of uncleanness.
Gen 2.18, Gen 1.28, 1 Cor 7.2, 1 Cor 7.9
It is lawful for all sorts of people to marry, who are able with judgment to give their consent; yet it is the duty of Christians to marry in the Lord; and therefore such as profess the true religion, should not marry with infidels, or idolaters; neither should such as are godly, be unequally yoked, by marrying with such as are wicked in their life, or maintain damnable heresy.
Heb 13.4, 1 Tim 4.3, 1 Cor 7.39, Neh 13.25-Neh 13.27
Marriage ought not to be within the degrees of consanguinity or affinity, forbidden in the Word; 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.
Lev.18, Mark.6.18, 1 Cor 5.1