A.T. Robertson Commentary Philippians 3:5

"circumcised the eighth day, of the stock of Israel, of the tribe of Benjamin, a Hebrew of Hebrews; as touching the law, a Pharisee;" — Philippians 3:5 (ASV)

Thinketh to have confidence (δοκε πεποιθενα). Second perfect active infinitive. Old idiom, "seems to himself to have confidence." Later idiom like Mt 3:9 "think not to say" and 1 Corinthians 11:16, "thinks that he has ground of confidence in himself."

I yet more (εγω μαλλον). "I have more ground for boasting than he" and Paul proceeds to prove it in the rest of verses 5,6.

Circumcised the eighth day (περιτομη οκταημερος). "In circumcision (locative case) an eighth day man." Use of the ordinal with persons like τεταρταιος (John 11:39). Ishmaelites were circumcised in the thirteenth year, proselytes from Gentiles in mature age, Jews on the eighth day (Luke 2:21).

Of the stock of Israel (εκ γενους Ισραηλ). Of the original stock, not a proselyte.

Benjamin (Βενιαμιν). Son of the right hand (that is, left-handed), son of Rachel. The first King, Saul (Paul's own Hebrew name) was from this little tribe. The battle cry of Israel was "After thee, O Benjamin" .

A Hebrew of the Hebrews (Εβραιος εξ Εβραιων). Of Hebrew parents who retained the characteristic qualities in language and custom as distinct from the Hellenistic Jews (Acts 6:1). Paul was from Tarsus and knew Greek as well as Aramaic (Acts 21:40; Acts 22:2) and Hebrew, but he had not become Hellenized.

A Pharisee (Φαρισαιος). In distinction from the Sadducees (Galatians 1:14) and he continued a Pharisee in many essential matters like the doctrine of the resurrection (Acts 23:6). Cf. 2 Corinthians 11:22.