St. Augustine On Circumcision

Saint Augustine

Accordingly, when you ask why a Christian is not circumcised if Christ
came not to destroy the law, but to fulfil it, my reply is, that a
Christian is not circumcised precisely for this reason, that what was
prefigured by circumcision is fulfilled in Christ. Circumcision was the type of the
removal of our fleshly nature, which was fulfilled in the resurrection of
Christ, and which the sacrament of baptism teaches us to look forward to
in our own resurrection. The sacrament of the new life is not wholly
discontinued, for our resurrection from the dead is still to come; but
this sacrament has been improved by the substitution of baptism for
circumcision, because now a pattern of the eternal life which is to come
is afforded us in the resurrection of Christ, whereas formerly there was
nothing of the kind.

Reply to Faustus the Manichaen. Book XIX. Paragraph 9.
In: Dods M (ed). The Works of Aurelius Augustine, Bishop of Hippo.
Edinburgh: T. & T. Clark. 1872. vol. 15, p. 334.

“Well, now, I should like to be told what there is in these ten
commandments, except the observance of the Sabbath, which ought not to be
kept by a Christian. . . . Which of these commandments would anyone say
that the Christian ought not to keep? It is possible to contend that it
is not the law which was written on those two tables that the apostle
[Paul] describes as ‘the letter that kills’ [2 Cor. 3:6], but the law of
circumcision and the other sacred rites which are now abolished” (The
Spirit and the Letter 24 [A.D. 412]).