To His Wife by Tertullian
Chapter II.--Marriage Lawful, But Not Polygamy.
We do not indeed forbid the union of man and woman, blest by God as the seminary of the human race, and devised for the replenishment of the earth and the furnishing of the world, and therefore permitted, yet singly. For Adam was the one husband of Eve, and Eve his one wife, one woman, one rib. We grant, that among our ancestors, and the patriarchs themselves, it was lawful not only to marry, but even to multiply wives. There were concubines, too, (in those days.) But although the Church did come in figuratively in the synagogue, yet (to interpret simply) it was necessary to institute (certain things) which should afterward deserve to be either lopped off or modified. For the Law was (in due time) to supervene. (Nor was that enough:) for it was meet that causes for making up the deficiencies of the Law should have forerun (Him who was to supply those deficiencies). And so to the Law presently had to succeed the Word of God introducing the spiritual circumcision. Therefore, by means of the wide licence of those days, materials for subsequent emendations were furnished beforehand, of which materials the Lord by His Gospel, and then the apostle in the last days of the (Jewish) age, either cut off the redundancies or regulated the disorders.