Seal of Righteousness

How is circumcision a seal of the righteousness of faith (Romans 4:11).  Augustine ( Contra Faustum ) says this:

Circumcision was performed on the eighth day.

The eighth day is the day of Jesus’ resurrection.

Jesus resurrection is for our justification (Romans 4:25).

Hence, “because this resurrection, which justifies us when we believe it, was symbolized by that circumcision on the eighth day, the apostle therefore says of Abraham, to whom it was first entrusted, ‘And he received the sign of circumcision as a sign of the righteousness of faith.’”