'Strictest' in the Bible

“I am a Jew, born in Tarsus of Cilicia, but brought up in this city, educated at the feet of Gamaliel according to the strictness of the law of our fathers, being ardent and passionate for God just as all of you are today.

They have known me for a long time, if they are willing to testify to it, that according to the strictest sect of our religion, I have lived as a Pharisee.

And in all things show yourself to be an example of good works, with purity in doctrine [having the strictest regard for integrity and truth], dignified,