“… to reach all the riches of full assurance of understanding and the knowledge of God's mystery, which is Christ, in whom are hidden all the treasures of wisdom and knowledge” (2:2). The Corinthian believers wanted to develop “wisdom and knowledge”, but Paul was worried that they were searching in the wrong direction. Some were teaching that denying themselves certain foods was the way to holiness, or strictly observing the Sabbath, or some other rule (v16-23). But all this was “nailed to the cross” so that we could know Christ personally (v14).
The food codes and rituals of the Old Testament were the “shadow” of God’s glory, but now we have the substance, Jesus Christ Himself (v17).