Circumcised the eighth day (περιτομῇ ὀκταήμερος)
Lit., eight days old in circumcision; or passing the eighth day. For the idiom, see on Joh 11:39, and compare Act 28:13. Converts to Judaism were circumcised in maturity: Ishmaelites in their thirteenth year. He was thus shown to be neither a heathen nor an Ishmaelite.
Of the stock of Israel
Not a proselyte, but of the original stock (γένους); not grafted into the covenant race. A descendant of Jacob, not an Idumaean nor an Ishmaelite. For Israel, see on Act 3:12, and compare Rom 9:4; Rom 11:1; Joh 1:47. Descended not from Jacob, the supplanter, but from Israel, the prince of God. See Gen 32:28.
Of the tribe of Benjamin
Not from one of the lost tribes, but from that which gave to Israel its first king; which alone was faithful to Judah at the separation under Rehoboam, and which had always held the post of honor in the army. See Jdg 5:14; Hos 5:8. Benjamin only of the twelve patriarchs was born in the land of promise. Mordecai, the deliverer of the Jews from Haman was a Benjamite. Paul's own original name, Saul, was probably derived from Saul the son of Kish, the Benjamite.
A Hebrew of the Hebrews (Ἑβραῖος ἐξ Ἑβραίων)
The (Hebrews) of the A.V. gives a wrong coloring to the phrase, as if Paul were claiming to be preeminently a Hebrew among other Hebrews. He means a Hebrew from (ἐξ) Hebrew parents. Rev., a Hebrew of Hebrews, which is no special improvement. The expression implies characteristics of language and manners. He might be an Israelite and yet a child of Greek-speaking Jews: but his parents had retained their native tongue and customs, and he himself, while understanding and speaking Greek, also spoke in Hebrew on occasion. See Act 21:40; Act 22:2.
The law
The Mosaic law. See on Rom 2:12. The validity of that law was the principle upheld by the Judaizers.
A Pharisee
See Act 23:6; Gal 1:14. Compare on the whole verse, 2Co 11:22.