John Gill Commentary Genesis 26:4

"And I will multiply thy seed as the stars of heaven, and will give unto thy seed all these lands. And in thy seed shall all the nations of the earth be blessed." — Genesis 26:4 (ASV)

And I will make your seed to multiply as the stars of heaven ,
&c.] Meaning in the line of Jacob especially, if not only; from whom sprung twelve patriarchs, the heads of so many tribes, which in process of time became very numerous, even as the stars of heaven: and I will give to your seed all these countries ;
which is repeated from (Genesis 26:3) for the greater confirmation of it: and in your seed shall all the nations of the earth be blessed ;
meaning in the Messiah that should spring from him, see (Genesis 22:18) .