Therefore, the promise is by faith that it might come to us as a free gift [by grace], so that the promise might be sure to all the descendants, not only to those who live by the Law but also to those who only believe as Abraham did. He is the father of all of us. (GWN)
That is why it depends on faith, in order that the promise may rest on grace and be guaranteed to all his offspring—not only to the adherent of the law but also to the one who shares the faith of Abraham, who is the father of us all. (ESV)
Therefore it is of faith that it might be according to grace, so that the promise might be sure to all the seed, not only to those who are of the law, but also to those who are of the faith of Abraham, who is the father of us all. (NKJV)