Why were the Corinthians not cashing in on God's wisdom?
The Corinthians were not cashing in on God's wisdom because they remained carnal. Paul contrasted the wisdom of men with the wisdom of God, yet these believers were still fleshly, so they did not access the fountain of divine wisdom that was theirs for the taking.
Les teaches that Paul had been constantly comparing the wisdom of men with the wisdom of God, yet the Corinthians remained so carnal that they were not cashing in on the fountain of wisdom that was theirs for the taking. Les applies it today: every believer can simply get into the Book and feast on it, but most won't. The excuse "I can't understand it" is not valid; it is not that difficult if you separate what is for the Jew from what is for the Gentile and compare Scripture with Scripture. God dealt with the Jew under Law, but deals with us today under Grace; Law and Grace are contrary principles and will not mix. Paul cries against legalism because we are not under Law but under Grace.