Genesis 17:12, commentary and pictures

Circumcision at eight days old was given as the sign, token, pledge, and requirement of the covenant with Abraham and his descendants, the condition by which a child became entitled to the blessings of that covenant. It marked Abraham's descendants as devoted to God and set apart from idolaters and other nations, it showed that God accepted them as His special people, and it pledged them to keep their part of the covenant by remaining separate and faithful to God. That separation was meant to guard them from idolatry and rebellion. When they mingled with surrounding nations they lost much of their holy character and fell into idolatry.

Had they kept that covenant and remained separate from idolatrous nations, they would not have gone down to Egypt. God would not then have needed to proclaim the law at Sinai with added directions to guard obedience to it, nor with its added judgments and statutes. The force of the requirement is seen in Moses, who at his wife's persuasion neglected the known duty of circumcising his youngest son. Such neglect by God's chosen leader lessened the force of the divine precepts upon the people.

He was entering the great peril of his mission to Pharaoh, where his life could be preserved only through the protection of holy angels. Living in neglect of that duty left him insecure and exposed to destruction until his wife herself performed the rite. The same rule holds just before the coming of Christ, when the righteous will be preserved through the ministration of heavenly angels. There will then be no security for any transgressor of God's law, since angels cannot protect those who disregard even one divine precept.