Deuteronomy 21:15 - Clarke's commentary and critical notes on the Bible

If a man have two wives, one beloved, and another hated, and they have born him children, both the beloved and the hated; and if the firstborn son be hers that was hated: One beloved, and another hated - That is, one loved less than the other. This is the true notion of the word hate in Scripture. So Jacob Hated Leah, that is, he loved her less than he did Rachel; and Jacob have I loved, but Esau have I Hated, that is, I have shown a more particular affection to the posterity of Jacob than I have to the posterity of Esau. See the note on Genesis 29:31. From this verse we see that polygamy did exist under the Mosaic laws, and that it was put under certain regulations; but it was not enjoined, Moses merely suffered it, because of the hardness of their hearts, as our Lord justly remarks Matthew 19:8.