We come to the cause of the problem that the Jews had - an uncircumcised heart. They had an outward sign but no inward reality to which the sign should have pointed.
We see that true religion is of the heart. It doesn’t matter how many outward rituals and acts we may perform as long as our heart remains cold and dead. We need the work of the Spirit to circumcise our hearts, so that our outward signs and performances will correctly arise from a right attitude within.
Finally, we understand that we can examine our hearts in this matter by their attitude to God’s law. We need to keep the law not for outward show and to earn righteousness with God but rather from an inward love for the law, put there by God’s Spirit and out of a desire to please God and to grow more like Christ, who kept the law perfectly.