Moses, a faithful servant of God, allowed the Israelites to divorce their wives for the hardness of their hearts (Deuteronomy 24:1-4), but God’s institution of marriage was one man and one woman from the beginning (IRENAEUS, TERTULLIAN, ORIGEN).
The early Christians differed in their understandings of the exception clause in Matthew 5:32. Some early Christians believed that a man was permitted to put away his wife for fornication (HERMAS, THEOPHILUS OF ANTIOCH, ORIGEN, NOVATIAN, LACTANTIUS), or adultery (TATIAN, TERTULLIAN, ORIGEN) not out of malice or bitterness, but rather with the intention of not having concord with sin, and to discipline the erring spouse in hope of leading them to repentance.
Some also applied “fornication” with reference to unlawful marriages, i.e., incestuous marriage (TERTULLIAN) or a marriage contracted after divorce from the first living spouse (IRENAEUS, CLEMENT OF ALEXANDRIA).
Some did not even mention the exception clause when discussing divorce and remarriage
(JUSTIN MARTYR, ATHENAGORAS, MARK MINUCIUS FELIX).
Elsewhere Jesus affirmed the one-flesh union (Matthew 19:4- 6; Mark 10:5-9; cf. Romans 7:2; 1 Corinthians 7:10-11) and the adulterous state of remarriage while the original spouse is alive (Mark 10:11-12; Luke 16:18; cf. Romans 7:3; 1 Corinthians 7:39). Therefore, all of the early Christian writers forbid remarriage after divorce.