As it turns out, circumcision, though not uncommon in the ancient world (the Egyptians even did it), was a very suitable symbol of their covenant with God. The English word means "to cut around", while the Hebrew word means, "to cut off." As Gen. 17:11 says, "You are to cut off the flesh of your foreskin and it shall be the sign of the covenant between Me and you." So among the reasons for this rite is that it is a symbol or sign of being in Abraham's (and God's) family.Abraham's following was likely growing following his war victory and rescue of Lot. He certainly was wealthy, and even had his own army. God then gave this covenant sign as a requirement to be part of Abraham's people. No sloppy agape here. If you were in, it was off; you had to deny yourself, and wear the sacrificial mark on your body. Talk about a stumbling block for conversion.
It is ironic that one who is circumcised is "cut off" from the world, while one who refuses to be circumcised gets "cut off" from God's people (Gen. 17:14). Abraham's faith and works went hand-in-hand. Circumcision of the flesh is a work to be followed by faith. While circumcision of the heart is a faith to be demonstrated by works.
The New Testament would later explain that while Abraham is the father of the Jewish nation, he is also the father of many nations. Those of us who demonstrate faith follow as children of Abraham, not necessarily circumcised in the flesh, but still circumcised in the heart. Moses would later instruct the Israelites in this manner, saying, "Circumcise your hearts" (Deut. 10:16). Just as Israel is to be separate from the nations, the New Covenant calls us to be separate from the world, grafted into Israel, circumcised in our hearts, and demonstrating our faith through works.
This is why the apostle John would say, "Do not love the world or anything in the world" (1 Jn. 2:15). We love what we are passionate about. Our heart is the instrument of which we speak when discussing one kind of passion. It figuratively needs to be cut off from the world. But likewise is circumcision related to another intrument of passion. In that sense, circumcision is the perfect picture that all of our desires must be yielded to God's glory.

