Deuteronomy 21:15-17--Inheritance Rights of the Firstborn

Deuteronomy 21:15-17
English Standard Version
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Inheritance Rights of the Firstborn
15 “If a man has two wives, the one loved and the other unloved, and both the loved and the unloved have borne him children, and if the firstborn son belongs to the unloved, 16 then on the day when he assigns his possessions as an inheritance to his sons, he may not treat the son of the loved as the firstborn in preference to the son of the unloved, who is the firstborn, 17 but he shall acknowledge the firstborn, the son of the unloved, by giving him a double portion of all that he has, for he is the firstfruits of his strength. The right of the firstborn is his.

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If we know the book of Genesis, this sounds a whole lot like the story of Jacob who wanted to marry Rachel (the one he had eyes for), but was tricked into marrying her older sister Leah first (apparently she didn't look all that pretty as it says she had "weak eyes" which is an idiom saying that she wasn't all that much to look at).  The rights of the firstborn son to receive his inheritance should not be affected by favoritism towards which wife the husband loved more.

Note that God doesn't not say that it's okay to have multiple marriages here, nor did He say that in the last passage, but He knows the situation will arise because the it has already come up early on in the book of Genesis where the hearts of people were wicked and they desired to hoard people, power, and possessions for themselves to make them feel like they were gods.  God's design was always one man and one woman forever.

So, God knows His people are going to sin in this way, but even in so doing, he wants the children to be protected and make sure that the firstborn son (which the LORD has used that phrase to refer to Israel already) will always receive his inheritance.  We'll see this also points to Jesus, the only-begotten Son of the Father and that Jesus will definitely receive His inheritance from the Father--His people which the LORD has been promising would be an inheritance unto Himself--which doesn't make much sense until we realize that God is Three-in-One and The Father is giving true Israel and the Church universal (all believers) to the Son as His Bride and His inheritance.  The Son will also be given the kingdom of all creation.  All of heaven and earth and even those under the earth will be His subjects and will bow before Him and worship Him.

The firstborn was to receive a double-portion (twice as much as the others)--no more, no less.  This also protects the rights of the other children so that the father could not play favorites between them or simply leave everything to the firstborn.  Whatever the firstborn got needed to be a double-portion of what each of the others individually got and the entire estate was to be divided between all the male children and the unmarried female children (we already covered this earlier that once a woman was married it was no longer the father's responsibility to provide for her, but if she was unmarried she was to inherit just like all her brothers.  But if she was married after she inherited, then the land was to go back to the nearest relative so that it would stay in the family and not change ownership to the new family/clan that she married into for their plots of land were an eternal inheritance to the families, clans, tribes, and the nation as a whole.)  All that I just said there was to say that we should not read into this that women were excluded.  We've already seen how the LORD made provision for them earlier.  (see Numbers 27 and Numbers 36 where this is discussed if you're interested in this--specifically the daughters of Zelophehad).

Again, this is a promise to Israel who the LORD called His "firstborn son"--because Israel was to show people Christ and the LORD already tried to treat Israel as He would treat the Son of God as true Israel should have been saved and made into the likeness of the Son, just like the Church is supposed to be today--and of course this is also the promise for Jesus, the Son of God.  No one is going to take away His inheritance and we are part of the inheritance if we have been made children of God by His salvation.