Genesis 17:12

Eight days; not before that time, because of the child's weakness and imperfection, and impurity too, Exodus 22:30 Leviticus 12:3, for which reason also beasts were not to be offered to God before the eighth day, Exodus 22:30. Every man-child in your generations, successively, until the Messias come, who shall circumcise your hearts, and change this ordinance for another. Bought with money of any stranger: these were of two sorts.

1. Children, who being entirely his possession, and having not understanding to discern, nor will to choose 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 Abraham's servants here, they were thoroughly instructed in religion, Genesis 18:19, and doubtless did willingly embrace it, and submit to this sacrament.