When God appeared to Abraham in Gen 17, He introduced Himself as the ALMIGHTY (El-Shaddai). This elaborate introduction was intended to introduce Abraham into an economy in God where all things are possible. However, for Abraham to partake of this economy he had to subscribe to the covenant of circumcision.
This is still valid today, however, circumcision for us is not physical. According to Phil 3:3, circumcision is the state of the heart where you put no confidence in the flesh - your earthly credentials. When you get to the end of yourself, that is the beginning of God.