Abraham walked with God because he "believed" that God existed, believed that God would keep the promises for a son, and went where God led him. When Isaac was a young lad, God reckoned Abraham's faith as righteousness, and He requested that Abraham offer his son as a sacrifice to prove his faith. Abraham proved that he would do anything that God requested of him, and God spared the life of Isaac. After his testing, God entered into a covenant with Abraham. God made several promises as His part of the covenant, and Abraham was to circumcise all males in his houshold and all male children on the eighth day born in his household. All who were circumcised, were under the covenant promises, but those not circumcised would be excluded from the covenant.
Now, we who are of the "faith", as the faith of Abraham, under the royal law of Christ's blood (He is the one we are to "hear" and "answer to") enter into a covenant relationship with God when we "believe" that God is, and that He is a rewarder of all those who "seek" Him, and that Jesus is the Son of God; God gives us, by His grace which is His good will toward man, promise of everlasting life with Him and we are to enter into that covenant relationship by baptism in the name of the Father, Son, and Holy Spirit, which is representative of Christ's death, burial, and resurrection, and then to rise from the waters to walk circumspectly, worthy to be called a son of God in His righteousness through the blood of His Son, our redeemer. All those who are baptized are under the covenant relationship, and those who are not baptized are excluded from that covenant.