God said so.... So history tells us. Why the Jewish ritual is done on the 8th day when newborns years ago were first able to clot is a mystery to me, but it feeds into the narrative that there is some benefit. Once circumcised, a male will never have to worry that the foreskin might tighten down like a tourniquet & amputate the end of his penis. There lots of pros & cons offered but 6k years of history matters.
Circumcision. Performed for many reasons:- 1) religion, for muslims, jews & some baptists. 2) father is circumcised, 3) reduce risk of urinary infections, especially in boys with urinary tract abnormalities, 4) avoid future problems with a tight foreskin, 5) reduce risk of hiv, 6) avoid penile cancer, 7) cosmetic. These can all be debated except for #1.
Circumcision is... ...Controversial. For jews and muslims it is considered a commandment from god. Other ethnic groups do it for various social, cultural, or perceived sanitary reasons. While most health benefits are debatable, strong evidence from africa indicates that circumcision reduces the risk of HIV infection in heterosexual men by 38-66%.