Charles Ellicott Commentary Acts 26:4

"My manner of life then from my youth up, which was from the beginning among mine own nation and at Jerusalem, know all the Jews;" — Acts 26:4 (ASV)

My manner of life from my youth.—The Apostle refers, of course, to the time when he first came up to Jerusalem to study the Law and the traditions at the feet of Gamaliel. (Compare his account of the same period in Galatians 1:14; Philippians 3:5–6.)

Know all the Jews.—The noun seems to be used in its more limited meaning, as including chiefly, if not exclusively, the Jews of Judea.