What does Les mean when he refers to Paul's writings?
It means the letters Paul wrote are not merely the product of his human intellect or theological ability. Paul was the man God used to put these truths in print, and his writings carry weight because they are the Word of God, written as he was moved by the Holy Spirit.
Les explains that when he mentions the writings of Paul, he is not talking about Paul as a man, his intellect, or his tremendous ability to express theological truths. He is talking about the man God used to put these things in print. Les also emphasizes that every writer of Scripture wrote as he was moved by the Holy Spirit. He illustrates this with a verse he thought might be in II Corinthians, where Paul's critics said his speech was contemptible and his presence was not impressive, yet they admitted his letters were weighty. Les says this means Paul's written letters were different from his verbal preaching, because they became the Word of God and therefore carried the weight and impact of Scripture.