Why does Les believe in and teach the Rapture of the Church?
The Rapture is taught because the Body of Christ is a distinct entity, called out from Gentiles after Israel rejected Messiah. It is insulated from God's dealings with Israel, so it must be removed before God resumes His Old Testament program with Israel, including the tribulation, King, and Kingdom.
Les teaches the Rapture because, after Israel rejected their Messiah, God brought up the Apostle Paul and began calling out the Body of Christ, primarily from among the Gentiles. Since this calling has nothing to do with the Old Testament program or the tribulation—which is tied primarily to the Jew—the Body of Christ is insulated from God's dealings with Israel before or after. Therefore, the Body of Christ must be off the scene before God can pick up dealing with Israel again. Les illustrates this by removing the Church section and backing up to the Old Testament economy: the coming of the Messiah, the tribulation, the King, and the Kingdom. When Israel rejected it, God went to the calling out of the Body of Christ, and it has to be raptured; then He will yet bring in the tribulation to Israel. Les also maintains that Romans 11:25 is the triggering mechanism for Christ's coming for the Church, though no time element is given.