Of circumcised persons. The abstract term is used for the concrete. See on Rom 11:7.
Who not only are - but who also walk
Apparently Paul speaks of two classes, but really of but one, designated by two different attributes. The awkwardness arises from the article τοῖς, erroneously repeated with στοιχοῦσιν walk, which latter word expresses an added characteristic, not another class. Paul means that Abraham received a seal, etc., that he might be the father of circumcision to those who not only are circumcised, but who add to this outward sign the faith which Abraham exhibited.