This statement, standing alone, is incomplete.
Paul had VAST knowledge - just not of the Savior and His plans.
Remember that he studied at the feet of Gamiel?
Remember what Festus said to him?
YES, a vast knowledge of the law when the knowledge that counts is the JESUS/THE LORD - and when he learned who Jesus is, he embraced Him when only knowing HIM in the spirit and not in the physical/flesh. We know HIM the same way.