Having knowledge of me from the first (proginōskontes me anōthen). Literally, “knowing me beforehand” (both pro and anōthen), from the beginning of Paul’s public education in Jerusalem (Knowling). Cf. 2Pe 3:17.
If they be willing to testify (ean thelōsin martureōin). Condition of third class (ean and subjunctive). A neat turning of the tables on the distinguished audience about Paul’s Jerusalem reputation before his conversion.
After the straitest sect (tēn akribestatēn hairesin). This is a true superlative (not elative) and one of the three (also hagiōtatos, Jud 1:20, timiōtatos Rev 18:12; Rev 21:11) superlatives in ̇tatos in the N.T. (Robertson, Grammar, pp. 279f., 670), though common enough in the lxx and the papyri. Hairesin (choosing) is properly used here with Pharisees (Josephus, Life, 38).
Religion (thrēskeias). From thrēskeuō and this from thrēskos (Jam 1:26), old word for religious worship or discipline, common in the papyri and inscriptions (Moulton and Milligan’s Vocabulary) for reverent worship, not mere external ritual. In N.T. only here, Jam 1:26.; Col 2:18.
I lived a Pharisee (ezēsa Pharisaios). Emphatic position. Paul knew the rules of the Pharisees and played the game to the full (Gal 1:14; Phi 3:5.). The Talmud makes it plain what the life of a Pharisee was. Paul had become one of the leaders and stars of hope for his sect.