Gal 3:29 29 And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise. Believers became believers as a result of a unconditional Promise God made to Abraham, Now in the above text Paul is writing to the Church, the Body of Christ, of which He is Head, and which He is Abraham's Seed Gal 3:16, So the Head of the Church, Christ, is Abraham's Seed ! He is writing to both jew and Gentile believers in Christ. Now how did and why did they become Believers of Abraham's Seed ? Its by an unconditional promise that God made to Abraham, in which God promised Abraham a believing seed, that is when God told Abraham this Gen 17:5 5 Neither shall thy name any more be called Abram, but thy name shall be Abraham; for a father of many nations[Gentiles] have I made thee. Now how is Abraham the Father to Gentiles, by Faith Gal 3:6-9 6 Even as Abraham believed God, and it was accounted to him for righteousness. 7 Know ye therefore that they which are of faith, the same are the children of Abraham. 8 And the scripture, foreseeing that God would justify the heathen through faith, preached before the gospel unto Abraham, saying, In thee shall all nations be blessed. 9 So then they which be of faith are blessed with faithful Abraham. Rom 4:16-17 16 Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all[Jew and Gentile Believers], 17 (As it is written, I have made thee a father of many nations,) before him whom he believed, even God, who quickeneth the dead, and calleth those things which be not as though they were. So this would be to him a believing seed, and this seed is nit Abraham's children according to the flesh, this we know by Rom 9:7-8 7 Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. 8 That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed. Its a Seed that Isaac was a Type of, Children of Promise, and thats why Paul wrote unto the Believers at Galatia, who belonged to Christ Gal 3:29 this statement Gal 4:28 28 Now we, brethren, as Isaac was, are the children of promise. Who are the brethren ? Its those who he wrote earlier this Gal 3:29 !