Adam Clarke on 1 Corinthians 2:7

The wisdom of God in a mystery - The Gospel of Jesus Christ, which had been comparatively hidden from the foundation of the world, (the settling of the Jewish economy, as this phrase often means), though appointed from the beginning to be revealed in the fullness of time. For, though this Gospel was, in a certain sense, announced by the prophets, and prefigured by the law, yet it is certain that even the most intelligent of the Jewish rulers, their doctors, scribes, and Pharisees, had no adequate knowledge of it; therefore it was still a mystery to them and others, till it was so gloriously revealed by the preaching of the apostles.