Thou shalt not commit adultery. Our second duty towards our neighbour is to respect the bond on which the family is based, and that conjugal honour which to the true man is dearer than life. Marriage, according to the original institution, made the husband and wife "one flesh" (Genesis 2:24); and to break in upon this sacramental union was at once a crime and a profanity.
Adulteresses and their paramours were in most ancient nations liable to be punished with death by the injured party; but the adultery of a married man with an unmarried woman was thought lightly of. The precept of the Decalogue binds both man and woman equally.
Our Lord's expansion of this commandment (Matthew 5:27-32) is parallel to his expansion of the preceding one (ib, 21-26). He shows that there are adulterous marriages in countries where the law gives a facility of divorce, and that without any overt act adultery may be committed in the heart.