Deuteronomy 25:6

“And it shall be [that] the firstborn that she beareth, etc.] To her husband’s brother, now married to her: shall succeed in the name of his brother [which is] dead; the meaning is, as the Targum of Jonathan, “he shall rise up in the inheritance in the name of his brother;” or, as Jarchi expresses it, “he shall take the inheritance of the deceased in the goods of his father;” that is, he shall have his part and share in the inheritance that the deceased brother would have had if he had lived, which would come to him by his father: that his name be not put out of Israel; that the family be not lost in Israel, and the inheritance belonging to it pass to another. This law was designed to keep…”

“The law of levirate marriage. The law on this subject is not unique to the Jews, but is found (see Genesis 38:8) in all essential respects the same among various Oriental nations, ancient and modern. The rules in these verses, like those upon divorce, do but incorporate existing immemorial usages, and introduce various wise and politic limitations and mitigations of them. The root of the obligation here imposed upon the brother of the deceased husband lies in the primitive idea of childlessness being a great calamity (compare Genesis 16:4; and note), and extinction of name and family one of the greatest that could happen (compare Deuteronomy 9:14; Psalms 109:12-15). To avert this the…”

“That his name be not put out - That a family be not lost. So this was a provision that the number of their families might not be diminished. Deuteronomy 25:9”

“the firstborn: Gen 28:8-10 that his name: Deu 9:14, Deu 29:20; Rut 4:10-12; Psa 9:5, Psa 109:13, brother's wife, or, next kinsman's wife, go up, Deu 21:19; Rut 4:1-7 Deuteronomy 25:8”