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.”  Circumcision was the sign that these were God’s people.  A sign that they were Jewish.  But the verse is interesting in that it does not make circumcision the most important thing.  Notice that Paul writing to the Romans says that it is faith by which we need to walk.  Also, Abraham had this faith before the circumcision.  His walk was by faith before he ever saw the promise.  Hebrews 11 tells us that Abraham obeyed when he was called to go out not knowing where he was going.  What faith!  He was content to dwell in tents waiting for the city whose builder and maker is God.  What faith!  We can point out some mistakes in the record of his life.  He was not perfect in all his dealings but Paul mentions Abraham in Romans and Galatians quoting from Genesis 15:6.  “And he (Abraham) believed in the LORD; and he counted to him for righteousness.”  He simply believed God.  He walked in the steps of faith.  Galatians 3:9 “So then those who are of faith are blessed with believing Abraham.”  Walking by faith is believing God and all He says He will do.