Which knew me from the beginning
From his youth, from his first coming to Jerusalem:
if they would testify;
what they know, and speak out the truth of things, they must say,
that after the most straitest sect of our religion I lived a
Pharisee;
there were three sects of religion among the Jews, the Pharisees, Sadducees, and Essenes; the first of these was the most exact, and came nearest to the truth of doctrine, and was the strictest as to outward holiness of life and conversation, and of this sect the apostle was; and according to it he lived, and that in such a manner, as not to be charged with any notorious crime; and indeed in his own, and very likely in the opinion of others, he was then blameless. (See Gill on Matthew 3:7).
(Essenes: A Jewish sect, who, according to the description of Josephus, combine the ascetic virtues of the Pythagoreans and the Stoics with a spiritual knowledge of the divine law. It seems probable that the same name signifies "seer", or "the silent, the mysterious". As a sect the Essenes were distinguished by an aspiration after the ideal purity rather than by any special code of doctrines. There were isolated communities of the Essenes, which were regulated by strict rules, and analogous to those of the monastic institutions of a later date. All things were held in common, without distinction of property; and special provision was made for the relief of the poor. Self-denial, temperance and labour--especially agricultural--were the marks of the outward life of the Essenes; purity and divine communication the objects of aspiration. Slavery, war and commerce were alike forbidden. Their best known settlements were on the north west shore of the Dead Sea. J.B. Smith one volume Bible Dictionary.)