Verse 15 is regarded as difficult by the commentators. T V Moore gives the various views of the verse. Some regards ‘one’ as the subject – ‘And did not one make [do it]?’. In this case the one is sometimes said to Abraham. This either makes the phrase a defence mentioned by the Jews – ‘Abraham took a second wife, so why shouldn’t we?’, or else it is Malachi stating this objection, only to shoot it down himself. Moore is scathing about this interpretation, saying there is no plausibility in such an objection, since it is similar to this case seen here, it does not explain all the words in the verse and it is not introduced as an objection.
Calvin sees it as referring to Adam and Eve and the original ordination of marriage which was one man and one woman (though God could have given Adam more than one wife). That divine ordination must be recognised. This view focuses on the divorce of the wife of the man’s youth.
Moore links the verse to verse 10 of this chapter, where the oneness of the Jewish people is argued. God created the nation and separated them from other nations into an isolated unity. He did not choose just one nation on account of his Spirit being exhausted, for the residue of the Spirit was [still] with him. He did it in order to create a godly seed, a seed separated from the corruption of the nations, from whom the Messiah would come. But the introduction of mixed marriages would violate this oneness and frustrate God’s purpose. This view focuses not so much on the divorce as on the marrying outside Israel.