The command is brief. Genesis has God tell Abraham that every male among his people is to be circumcised at eight days old, and that a male who is not has broken the covenant. Everything procedural is rabbinic.
The timing is unusually immovable. The eighth day displaces the Sabbath, on which cutting is otherwise forbidden, and it displaces the Day of Atonement. A boy born at twilight, where the boundary between one day and the next is genuinely uncertain, is circumcised late rather than early, on the reasoning that the ninth day is a delay while the seventh is a wound inflicted outside the covenant altogether.
What does move it is the child. An infant who is jaundiced, feverish or underweight waits until he is well, and this is not treated as a concession but as law: danger to life sets aside almost the whole of Jewish practice. The Talmud goes further and rules that a woman who has lost two sons to the procedure does not circumcise the third, and extends the exemption to her sisters' sons. The tradition worked out, in late antiquity, that the risk ran in families.
The operation has three named parts. The foreskin is cut; the inner membrane is drawn back so that the corona is fully uncovered; and blood is drawn from the wound. The third part, metzitzah, is the one that has caused trouble in the modern period, because a minority of ultra-Orthodox practitioners perform it by direct oral suction. New York City health authorities documented neonatal herpes transmissions traced to the practice and in 2012 required written parental consent before it; the requirement was withdrawn in 2015 in favour of an agreement with community leaders, and the underlying disagreement about whether the city may regulate it at all has not gone away.
Around the surgery sits a ceremony that is mostly about welcome. A sandek holds the child; an empty chair is set for Elijah; the boy receives his Hebrew name in the same breath as the covenant. The rite is not and has never been argued by the tradition as a health measure. It is a permanent mark made on a body that could not consent, and the permanence is the entire point being made.