Thepromis recalled through faith

Romans 4:10-16
Faith was counted to Abraham as righteousness. It was not after, but before he was circumcised. He received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised.
It was not through the law that Abraham and his offspring received the promise that he would be heir of the world, but through the righteousness that comes by faith. For if those who depend on the law are heirs, faith means nothing and the promise is worthless, because the law brings wrath. And where there is no law there is no transgression.
Therefore, the promise comes by faith, so that it may be by grace and may be guaranteed to all Abraham’s offspring—not only to those who are of the law but also to those who have the faith of Abraham. 
Why?
The promise recalled through faith and it is not by the law.
Abraham is the father of all who received the grace of the Lord through faith.
How?
The promise recalled through faith.