Why do Jews circumcise?

Throughout Jewish history, circumcision signifies the covenant between the Jewish people and God.

Brit mila (photo credit: MARC ISRAEL SELLEM/THE JERUSALEM POST)
Brit mila
(photo credit: MARC ISRAEL SELLEM/THE JERUSALEM POST)
Male Jews are circumcised when they are eight days old, as per the Biblical tradition listed in the Book of Genesis (17:12) and Leviticus (12:3).  God commanded Abraham to circumcise all the males of his household, himself, and Ishmael his son. Throughout Jewish history, circumcision signifies the covenant between the Jewish people and God, as the text reads (Genesis 17:11), “You shall circumcise the flesh of your foreskin, and that shall be the sign of the covenant between Me and you. 
The Midrash relates that Turnus Rufus, the Roman governor of Palestine, asked the great sage, Rabbi Akiva – “If God wanted man to be circumcised, why didn’t he create man in that way (already circumcised)? Rabbi Akiva responded, “Because God gave the commandments to the Jewish people to purify them.” That is, God has created an incomplete world, and Man has been assigned to help complete the task.