There is somewhat beside the moral sense of this passage, of a spiritual signification connected with it to be understood. As in the case of the great Father of the Israelites, the LORD himself was pleased to determine even before the children were born, that the elder should serve the younger, lest Israel should be led by caprice to do that which the LORD in wisdom was only competent to determine, the LORD passeth it into a law to prevent all abuses on this ground. But the Reader will not forget to observe the extent of the precept in this instance, it reached only to temporal possessions. LORD, let that be my portion which Paul speaks of: Ephesians 1:3.
Related Commentaries of Deuteronomy 21:15
Deuteronomy 21:15-17
15 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:
16 Then it shall be, when he maketh his sons to inherit that which he hath, that he may not make the son of the beloved firstborn before the son of the hated, which is indeed the firstborn:
17 But he shall acknowledge the son of the hated for the firstborn, by giving him a double portion of all that he hath: for he is the beginning of his strength; the right of the firstborn is his.