What is the clearly divided division between Israel and the Gentiles and the Body of Christ that men have mixed up?
The clearly divided division is God's separate dealings: His program with Israel versus His program with the Gentiles and the Body of Christ. Men have mixed them by tainting the apostle's distinct revelation with what the twelve learned from Jesus, instead of keeping God's dealings with Israel and the Gentiles/Body of Christ unmixed as God intended.
Les explains that the Holy Spirit deliberately prevented this man from being influenced by what the twelve had learned at Jesus' feet for three years. The Lord Jesus in glory had something totally different to show him and did not want it mixed up. Men, however, are adept at mixing it and have been mixing it ever since the apostle left the sea. Les says his aim is to unmix it and restore the clearly divided division between what God did with Israel and what He is doing with the Gentiles and the Body of Christ. That is why the apostle conferred not with flesh and blood and did not go up to Jerusalem to those who were apostles before him, though he never took away Peter's or the eleven's authority.
To reveal his Son in me, that I might preach him among the heathen; immediately I conferred not with flesh and blood:
Neither went I up to Jerusalem to them which were apostles before me; but I went into Arabia, and returned again unto Damascus.