Oh cool. This should clear it up for you then...
Paul wrote to the Galatians:
"Now to Abraham and his Seed were the promises made. He does not say, “And to seeds,” as of many, but as of one, “And to your Seed,” who is Christ."
This is a direct quote from the Old Testament from several places...
Genesis 12:7 "“To your descendants I will give this land.”
Genesis 15:18 "“To your descendants I have given this land, from the river of Egypt to the great river, the River Euphrates..."
Genesis 24:7 "‘To your descendants I give this land"...
Genesis 26:4 “And I will make your descendants multiply as the stars of heaven..."
Genesis 35:12 “The land which I gave Abraham and Isaac I give to you; and to your descendants after you I give this land.”
I could go on.
Literally EVERY time "descendants" is written it is the Hebrew word zera. That is the Hebrew word for "seed" or "seeds". This is not strange even in English. We may have a bag of seed OR we may have a bag of seeds. Both are correct. So we need some clarification.
Paul, by inspiration of the Holy Spirit, instructed us to read "descendants" as "Seed"; singular meaning Christ.
“And to your Seed,” who is Christ.
The natural Jews are not the people of promise. Only those in Christ are of the Seed of Christ. They will inherit the promises.