What did the Holy Spirit help the Corinthians understand when Paul preached?
The Holy Spirit helped the Corinthians understand that they were sinners for whom Christ died and rose from the dead. When Paul preached the simple gospel of Christ, the power of God—not human eloquence—brought them out of paganism and gave them understanding.
Les explains that Corinth was close to Athens, so the Corinthian believers were surrounded by the philosophy and paganism of Athens. They were used to hearing philosophers with smooth talk and big words. Paul, however, said he would not come with a bunch of smooth talk or the big long words of the philosophers; he came with power. Les teaches that it was not Paul's fast talking or language that brought these people out of paganism, but the power of God when he preached the simple gospel of Christ. The Holy Spirit helped them understand that they were sinners for whom Christ died and rose from the dead. This agrees with verse 20: the kingdom of God is not in word but in power.