It’s quite interesting to read the posts in this conversation from my perspective. For instance, where you (non-Jews) see a story about circumcision at Exodus 4:24-26, Jews see something different. Also, people from a Christian world view (whether religious or not) tend to read the statements in the Bible as literal, as if God commanded the practice of circumcision (which is not likely at all).
Exodus 4:24-26 is a parallel of the episode of Genesis 32:25-33. The stories both involve a Jewish hero, in Exodus it is Moses, in Genesis it is Jacob. Both stories involve an attack by a divine being while journeying from one land to another, Jacob by an angel, and Moses by God. Both stories have the divine beings “losing” the fight, with Jacob refusing to stop fighting and with Zipporah using blood as a ransom.
It is not certain if this is a story of an actual circumcision because there seems to be a play on words in the expression “Bridegroom of Blood” which can mean “protect” as well as “circumcise.” The expression “Bridegroom of Blood” may be a name given to Moses much as Jacob gets renamed Israel. The saving power of the blood in the attack on Moses foreshadows the saving power of the blood used by the Israelites on their doorposts on Passover.
As for the episode in which Saul asks David for “foreskins” as a substitute for a bride-price at 1 Samuel 18:25, the expression was a contemptuous (and somewhat bigoted) way of referring to the Philistines and their lives. As the Philistines were not circumcised, and this was considered detestable to the Jews, this was a way of asking for “proof” that David had slaughtered Philistines. (Compare 1 Samuel 14:6 for a similar contemptuous use of the term toward the Philistines.) The issue is not really the foreskins but the insult of referring to proof of their lives in being reduced to counting foreskins of the dead.
Circumcision was not exclusive to the Jews, but was common as a rite in neighboring cultures and nations. It appears to have been connected with the nuptial ceremony of these peoples. In line with this, the ancient Hebrews picked up the tradition and at first followed the more primitive custom of circumcision at the age of puberty, a rite of passage to manhood. It appears it was sometimes reserved to the age of warrior acceptance in Israel before their settling in the Promised Land. It was only after settling that the rite was transferred to the eighth day after birth, the Torah being only a regulating factor to the custom and less the source of something that was adopted from the custom of the surrounding heathen world.
In other words, this seems to be another thing the Jews did (like plural marriage and slavery) that they had previously adopted from the surround cultures as norms and that the Mosaic Law merely allowed by regulation. As always, the language of Scripture makes these practices sound like inspired instruction from heaven but critical examination of Hebrew history offers contrary evidence.