Why does Paul in Romans 4:11 describe circumcision as a ‘seal of the righteousness which he had by faith’, and what corresponds to it in the New Testament?

This text is from a letter written by David Gooding in 1999.

In the ancient world, when somebody made a solemn statement or a promise, it was then sealed—that settled the matter. So when Abraham was justified by faith, God put his seal upon that fact by giving Abraham the token of circumcision (see Romans 4:11).

Circumcision was not a condition of being justified. It did not contribute to his justification. But it was a token given by God that he had been justified.

According to the New Testament, we likewise, when we believe, are given a seal by God. That seal is the gift of the Holy Spirit (see Ephesians 1:13; see also Philippians 3:3).

Yours very sincerely in Christ,