“And if yee be Christs, then are ye Abrahams seed, and heires according to the promise.”
1611 King James Version (KJV)
3:29 If ye are Christ's - That is, believers in him.
Ga 3:29 If ye [be] Christ's, then are ye Abraham's seed, and heirs according to the promise. As Christ is the seed of Abraham, all in Christ become the spiritual seed of Abraham, and hence heirs of the promise to Abraham's seed.