As was the case in the time of Nehemiah and Ezra, so it was in Malachi’s day that the men of Judah were divorcing their godly wives, in order to enter into marriage with pagan women. But a marriage between the Jews and pagans would confuse the children born in that marriage, insofar as the father worshipped Yahweh, whereas the mother worshipped her pagan gods. The children born in a mixed-faith marriage would be raised in an environment where more than one true God was worshipped, which not only could but most likely would result in the children failing to serve Yahweh only and faithfully.
15 Did he not make them one, with a portion of the Spirit in their union? And what was the one God seeking? Godly offspring. So guard yourselves in your spirit, and let none of you be faithless to the wife of your youth.