What does Genesis 17:13 mean?
This verse repeats the requirements detailed in verse 12. Every male of Abraham's household, both now and for all generations, is to be circumcised. Male children born into this extended family, including those not related by birth or marriage, are to be circumcised at eight days old. Newly acquired male slaves are also to be circumcised. God spells out His intention that His covenant with Abraham and with the generations to follow would be "in your flesh." They would carry this reminder of their covenant relationship with God with them on the most intimate part of their bodies, one generation after another, forever.The following verse will help to explain how important this sign is meant to be. Those who refuse to take on this sign—men who will not take this covenant step—are to be "cut off," or separated, from God's chosen people. Those who refuse to identify with God through circumcision will not be allowed to partake in His covenant blessings.
This, however, is a requirement specific to this covenant, and for this covenant people. Circumcision is not a requirement for those who are not part of the nation of Israel. In fact, in the New Testament, references to circumcision will become shorthand for those who attempt to earn salvation by good works, rather than by faith (Acts 11:2; Galatians 6:12).