Pierre Marcel on the nature of circumcision in the Old Testament. Italics are his.

Circumcision thus represents the obligation resting upon him who received this sign, in authentication  of this promise, to circumcise his heart and living according to the covenant…

Circumcision, therefore,  truly has a spiritual meaning in perfect harmony with the covenant of grace, itself spiritual, of which it is the sign and seal. The device whereby an attempt is made to divide the Abrahamic covenant into two or three covenants distinct from each other [by Baptists], in order that, to suit the convenience of a certain people, a “carnal” element may be inserted into it, has no justification…

All that we have today in our sacraments the Jews had formerly in theirs, namely, Jesus Christ and His spiritual riches. The efficacy of the sacraments of the Old Testament is identical with that of the sacraments of the New, because they are equally signs, seals, and confirmations of the good will of God for the salvation of men. There is, it is true, a difference between the sacraments as regards outward appearance, but they are identical as regards their internal and spiritual significance. The signs have changed, while faith does not change.