Marriage is to be between one man and one woman. It is not lawful for any man to have more than one wife, or for any woman to have more than one husband, at the same time.
Marriage was ordained for the mutual help of husband and wife, for the increase of mankind with a legitimate issue [= progeny], and for preventing uncleanness.
It is lawful for all sorts of people to marry if they are able with judgment to give their consent. But it is the duty of Christians to marry in the Lord, and therefore those who profess the true religion should not marry with infidels or idolaters. Nor should those who are godly be unequally yoked by marrying with those who are wicked in their life or who maintain heretical teaching condemned to judgment.
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 that such persons may live together as man and wife.