Well, you can thank Abraham for circumcision. Blame him. He agreed to the deal.
When Abraham was 99 years old he confirmed the covenant that he had made with God… and that God had made with him many years earlier. Genesis 17 tells the story: God approached Abraham (whose name had been Abram until this moment) and declared once again his promise to make Abraham the father of many nations and that the land (of Israel) would belong to his descendants. That was God's end of the deal. Abraham's responsibility was to "walk with God and be blameless."
As a way to demonstrate the human side of the deal, God informed Abraham that any male who wanted to be a part of this deal had to be circumcised. If a descendent of his was not circumcised he would be cut off from the covenant. Either way you get cut.
So Abraham immediately applied this sign to himself… a procedure I imagine that most 99 year-old men wouldn't really want to go through… and he also applied this sign to all the men in his household (including grown male servants, foreign men, and his 13-year-old half-illegitimate son, Ishmael). I assume it was for the most part a voluntary procedure. Though I'm not sure how excited everyone was… but this is what we are told happened. Maybe some strong whiskey and very sharp knives got them through it? "Turn your head and cough" must have been quite a cutting remark that day. Certainly the barber shop knew what you meant when you asked, "Just a little off the top, please."
Now I suspect that many people today consider the Bible to be a bit antiquated because it talks fairly regularly about about circumcision. I also suspect that circumcision makes a lot of people squirm. It's not a typical dinner conversation topic. That's too bad in a way… because circumcision really is quite a powerful symbol of what a relationship with God is supposed to be. Circumcision was a severe step of faith that prevented someone from being severed from God.
But it is not the symbol that saves… Just as a road sign cannot actually get a person to their destination… it merely points the way. This sign only applied to men (and I believe it is significant that this symbol of faithfulness was borne on the part of the male anatomy that men generally struggle to keep faithful). This sign did not apply to women… though they would have had an intimate reminder of the covenant with God every time their sons were circumcised or they saw their husbands naked. But clearly the sign of circumcision did not apply directly to 1/2 of Abraham's descendents… and therefore it never was the means by which someone was "saved". A sign can not get someone somewhere… it merely points the way.
Consider what Paul says in Romans 4:9-12. Paul has already in this chapter introduced Abraham as an example of someone who God credited as a "righteous" person not because of his good religious piety but because of his faith in God. The objection to this statement perhaps could be that Abraham was "obedient" and did many good things because God told him to do so (e.g. circumcision)… and therefore Abraham was called "righteous". But it is fair to say that "righteousness" is not a complete adjective describing Abraham's life… a life of general goodness mixed with significant moments of sin. To this argument, Paul says…
NIV 9-12 Is this blessedness only for the circumcised, or also for the uncircumcised? We have been saying that Abraham’s faith was credited to him as righteousness. Under what circumstances was it credited? Was it after he was circumcised, or before? It was not after, but before! And he received circumcision as a sign, a seal of the righteousness that he had by faith while he was still uncircumcised. So then, he is the father of all who believe but have not been circumcised, in order that righteousness might be credited to them. And he is then also the father of the circumcised who not only are circumcised but who also follow in the footsteps of the faith that our father Abraham had before he was circumcised.
Paul makes it clear that Abraham was "credited" as "righteous" before he started really "doing" things for God. The outer sign of belonging to God took place after the inner reality of faith in God had started to take root in Abraham. Inside out faith.
Is this true? Was Abraham "saved" or "justified" or "made righteous" by God before he applied this dramatic sign? Well, circumcision happened in Genesis 17 when Abraham (Abram) was 99 years old. We are told in Genesis 15:6, when Abram was many years younger, "Abram believed the LORD, and he credited it to him as righteousness."
A circumcised life is simply meant to display a heart set on God.