SEV Biblia, Chapter 21:15
¶ Cuando algún varón tuviere dos mujeres, la una amada y la otra aborrecida, y la amada y la aborrecida le hubieren dado a luz hijos, y el hijo primogénito fuere de la aborrecida;
Clarke's Bible Commentary - Deuteronomy 21:15
Verse 15. 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 "Gen. xxix. 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 Matt. xix. 8.
John Gill's Bible Commentary
Ver. 15. If a man have two wives , etc.] Which is supposed, but not approved of, though permitted because of the hardness of men’s hearts; for it was not so from the beginning, when only one man and one woman were created, and joined together in marriage; but as it was connived at, and become customary, a law is made to prevent confusion, and preserve order in families: one beloved and another hated ; or less loved, yet continued his wife, and not divorced. Aben Ezra observes, this follows upon the former, because it is there said, that though first he had a desire to her (the captive beautiful woman), yet afterwards had no delight in her: and they have borne him children both, the beloved and the hated ; as Rachel and Leah did to Jacob, who were, the one very much beloved by him, and the other less: and if the firstborn son be hers that was hated ; or not so much beloved as the other, as was the case in the above instance.
Matthew Henry Commentary
Verses 15-17 - This law restrains men from disinheriting their eldest sons withou just cause. The principle in this case as to children, is still bindin to parents; they must give children their right without partiality.
Original Hebrew
כי 3588 תהיין 1961 לאישׁ 376 שׁתי 8147 נשׁים 802 האחת 259 אהובה 157 והאחת 259 שׂנואה 8130 וילדו 3205 לו בנים 1121 האהובה 157 והשׂנואה 8130 והיה 1961 הבן 1121 הבכר 1060 לשׂניאה׃ 8146