Matthew Poole and continuators on Genesis 17:12

12 And he that is eight days old , shall be circumcised among you: every man-child in your generations , he that is born in the house, or bought with money of any stranger , which is not of thy seed.

Not before that time, because of the Childs weakness and imperfection, and impurity too, Exod. 22. 30. Levit. 12. 3. for which reason also Beasts were not to be offered to God before the eigth day, Exodus 22. 30.

Successively until the Messias come who shall circumcise your hearts, and change this Ordinance for another.

These were of two sorts, 1. Children, who being entirely his possession, and having not understanding to discern, nor will to chuse or refuse, were to be circumcised. 2. Grown persons, who were not to be compelled to be circumcised, but if they refused it, were not to be permitted to dwell in his Family, lest they should infect others, but were to be sold to strangers, as the Hebrew Doctors teach. But as for Abrahams Servants here, they were thoroughly instructed in Religion, Gen. 18. 19. and doubtless did willingly embrace it and submit to this Sacrament.

Marginal references: Heb. a son of eight days.; Levit. 12. 3. Luke 2. 21. John 7. 22.