It has everything to do, Christ, the Head of the Church is Abraham's Seed ! You deny that as well ? Gal 3:16
16Now 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.
Now is that Christ the same as this one ? Eph 5:23
23For the husband is the head of the wife, even as Christ is the head of the church: and he is the saviour of the body.
Apostle paul stated that the promise was made to the seed (singular) of Abraham, in that the coming Messiah would be the One sent from God thru which all on earth would be blessed!
those who place who have faith like Abraham, who trust in his seed the Messiah, would be blessed and part of the family of God!
the Lord saves ALL through the atonement of Jesus upon the Cross, but God has His OT believers under Old Covenant, NT believers under new Covenant in the Church, those to be saved after the Rapture etc!