What does Genesis 17:14 mean?

In the previous verses, God revealed a requirement of His covenant relationship with Abraham and with all the promised generations to follow. Every male, related in any way to Abraham, even every male servant, must be circumcised. New male children must be circumcised at eight days old. Now God emphasizes that this sign of the covenant between God and His people through Abraham is absolutely necessary. Any uncircumcised male is out of the covenant. Period. If he will not be cut in the foreskin of his flesh, he will be cut off from his people. God's people through Abraham must be circumcised or they will not be God's people.

Though circumcision has now become a routine practice in many parts of the world for completely non-religious reasons, it's important to note that this requirement of circumcision is not given in the New Testament to those who come into God's family through faith in Christ. It is not specifically forbidden, but Paul emphasized that salvation under the new covenant was through faith in Christ and not through covenant circumcision (Galatians 5:1–6). Instead, Paul wrote in Romans 2:29 of the need for a "circumcision of the heart" by the Holy Spirit, to be set apart for God inwardly and not merely outwardly.

Having said that, circumcision was absolutely required by God as an act of faith and obedience for His people through Abraham.