"They know that I lived as a Pharisee": see the note to Acts 22:3. The Apostle calls the teaching of the Pharisees the strictest teaching in the Hebrew confession. In its pure form it truly was such, as a purely conservative teaching about the truths of faith, especially in comparison, for example, with Sadducean teaching.
True, it had already gone to extremes in interpreting certain ordinances of the law; Mt 15:3 and following, and parallels. It also went to extremes in applying certain legal ordinances to life; Mk 7:3 and following, and parallels. Yet these very extremes flowed from the strictness of the teaching. Moreover, the Apostle is not speaking about the extremes, but about the general character.
The hypocrisy, pride, and other vices of life for which the Lord Jesus judged the Pharisees so strictly were abuses of the strictness of the teaching. They also belonged to individual members of the Pharisaic sect, not to the whole sect in itself.
The best representatives of the sect were both strict and honest, such as Nicodemus, Gamaliel, and others. In any case, the Apostle could call the teaching of this sect the strictest in the good sense of the word. Such, like the mentioned representatives of this sect, Saul undoubtedly was when he belonged to it.
"They know this," the Apostle adds, "if they are willing to testify," that is, if they do not wish to hide or deny it. The qualification rests on the fact that it is disadvantageous for the Jews to testify to all this. All this concerns his honor and the proper evaluation of his present case. Neither is advantageous to them, and perhaps they will not wish to testify.