Genesis 17:11

You shall, either by yourselves, or by the ministry of others, with respect to infants. That part of the body was chosen, because the effects of sin first appeared there; and because a part of the Hebrews' creed was, that Christ should be born of the family of Abraham. --- A sign that Abraham had agreed to the covenant with God, and to be a memorial of his faith and justice, Romans iv. 2; to distinguish also the faithful from infidels; to purge away original sin in male children, eight days old; and to be a figure of baptism. (Menochius) (Tirinus) --- God always appoints some sign of his covenants, as Jesus Christ instituted the holy sacrament of his body and blood, under exterior appearances, to assure us of his new alliance with Christians. (Calmet) --- The sacraments of the old law caused grace, only by means of faith in the Redeemer, of which they were signs. (St. Augustine, de Nupt. ii. chap. ultra[last chap.]) In this sense, the holy fathers assert, that circumcision remitted original sin to those who could receive it; though some think, it was only a bare sign or distinctive mark of the Jews. (Calmet) --- It is far beneath our baptism, which is more easy, general and efficacious; as the Christian sacraments are not like those of Moses, weak and needy elements. (Galatians iv. 9; St. Augustine ep. 158, ad Jan.; Psalm 73, &c.) (Worthington)