"In the Old Testament, divorce was permitted under certain circumstances, but it was not something that God desired or approved of. Jesus is emphasizing that divorce and remarriage are not to be taken lightly and should only be considered in the most extreme situations."

Was divorce permitted or merely tolerated?

Was polygyny permitted or merely tolerated?

Are either permitted or tolerated today?

When (and where in the Bible) does Jesus say we should consider remarriage?

'The phrase "dealing treacherously" in Malachi 2:14 refers to a person who is unfaithful to their spouse and breaks their marriage covenant. This is similar to the concept of adultery that Jesus mentions in Luke 16:18. Both verses are warning against the serious sin of infidelity and the breaking of the marriage covenant.'

Is infidelity something that in itself ends a marriage? Is adultery?

'In Malachi 2:14, God reminds the Israelites that he has been a witness to their marriage covenant and that they have committed a sin against him by dealing treacherously with their spouses. Despite this, the wife is still considered a companion and the wife of their covenant.'

Makes sense. Even though the wife has been dealt with treacherously by her husband, she's still the due all the entitlements as his wife?

Sounds a bit like Israel being metaphorically married to God despite idolatry:

Jeremiah 3:1,13-14: "They say, If a man put away his wife, and she go from him, and become another man's, shall he return unto her again? shall not that land be greatly polluted? but thou hast played the harlot with many lovers; yet return again to me, saith the LORD. ... Only acknowledge thine iniquity, that thou hast transgressed against the LORD thy God, and hast scattered thy ways to the strangers under every green tree, and ye have not obeyed my voice, saith the LORD. Turn, O backsliding children, saith the LORD; for I am married unto you: and I will take you one of a city, and two of a family, and I will bring you to Zion:"

"In biblical teaching, there are limited reasons for ending a marriage. Adultery is one of the reasons that is considered legitimate for ending a marriage. However, even in such a case, it is not required that the marriage ends, and forgiveness and reconciliation are encouraged whenever possible. Apart from adultery, other reasons that could potentially end a marriage include abandonment, physical abuse, and unrepentant ongoing sin."

Where does the Bible discuss these reasons for ending a marriage?