John Chrysostom
"Circumcised on the eighth day." First he sets forth what they especially boasted in, circumcision. Then he says, "of the stock of Israel." Both show that he was neither a sojourner nor descended from sojourners. From the words "circumcised on the eighth day," it is clear that he was not a sojourner. From the words "of the stock of Israel," it is clear that his parents were not sojourners either.
But lest you think that "of the stock of Israel" means from the ten tribes, he says, "of the tribe of Benjamin." Therefore he was from the most honored tribe, because portions of the priests were in that tribe's inheritance.
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"A Hebrew of Hebrews." By this he shows that he was not a sojourner, but from honorable Jews of old. One could be from Israel and yet not a Hebrew of Hebrews, since many had already allowed their race to decline and had forgotten their language by mixing with other peoples.
Thus he shows here either this purity itself, or the special nobility of his origin.
"As to the law, a Pharisee." Then he passes to what belonged to his free will. Everything said above was involuntary. It did not depend on him to be circumcised, to be of the stock of Israel, or of the tribe of Benjamin.
Yet even in this respect he had more advantages, although many shared them. In what, then, was he "more"? Certainly in this also: that he was not a sojourner, that he was from the most honored tribe, and from ancient ancestors such as few had.
But since all this was involuntary, he passes to acts of choice, where this "more" is visible: "as to the law, a Pharisee; as to zeal, a persecutor of the Church of God" (v. 6).