Romans 4:12 And the father of circumcision to them who are not of the circumcision only, but who also walk in the steps of that faith of our father Abraham, which he had being yet uncircumcised. 13 For the promise, that he should be the heir of the world, was not to Abraham, or to his seed, through the law, but through the righteousness of faith. 14 For if they which are of the law be heirs, faith is made void, and the promise made of none effect:
Do we walk in the faith that came from Abraham? No, we walk in that faith that is the faith of Christ. We do not pass down faith to one another.
Romans 1:17 For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith.
We walk after that faith that reveals righteousness. We walk after the gospel of Jesus Christ. This was the same walk that Abraham walked. We do not walk in the personal faith that was Abraham’s, we walk in Christ. Each of us are given faith as the source of revelation to that faith which is Christ. Abraham is the father, or the example of this. Remember, this promise of the coming faith was given to Abraham as he was yet to be physically circumcised. Paul continuously wants to show how works or conditions do not matter. Salvation came to the circumcised just as it came to the uncircumcised. There are not two ways to God. There is but one way.
John 14:6 Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.
John 10:9 I am the door: by me if any man enter in, he shall be saved, and shall go in and out, and find pasture.
Circumcision was given as a sign of something yet to come, Romans 4:11. These promises were not given through the law. God did not give Abraham a rule or set of rules to follow to receive the promise made by God. The promise of him being an heir would come through the righteousness of faith, the law of faith. If this promise could come by the law, then why would Christ have to come at all. If we could do it by the law, then the work/death of Christ is not necessary. Salvation was conditioned on what God would fulfill in Christ, not on what He would fulfill in man. We play no part in salvation than to be heirs by grace, purchased with the blood of Christ. It was freely and graciously bestowed upon us. It was without condition on our parts, but upon His part a huge price was paid. If we are made heirs by following the law or any condition, then the promise God made to Abraham is of none effect.