The promises were made to Abraham and to his offspring. He did not say, "and to descendents," as if to many, but instead, as if to one, he said, "and to your offspring," who is Christ
Other versions
King James Version
Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ.English Standard Version
Now the promises were made to Abraham and to his offspring. It does not say, "And to offsprings," referring to many, but referring to one, "And to your offspring," who is Christ.New International Version
The promises were spoken to Abraham and to his seed. The Scripture does not say "and to seeds," meaning many people, but "and to your seed," meaning one person, who is Christ.