Concerning zeal, persecuting the church; concerning the righteousness which is in the law, blameless.
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Augustine of Hippo
AD 430
Before his conversion Paul fulfilled the law conspicuously, either through fear of the people or of God himself, even if he may have offended the law in his internal affections. But he was fulfilling the law through fear of punishment, not through love of righteousness.
“If then it was because of my good breeding and my zeal and my way of life, and I had all the things that belong to life, why,” he says, “did I let go those lofty things, unless I found that those of Christ were greater, and greater by far?” Homily on Philippians.