Why is the rest of the Bible still not inappropriate when Paul's letters are the main focus?
Paul's letters are the primary source for Church Age fundamentals, but that does not make the rest of Scripture inappropriate. Paul himself writes that all Scripture is inspired of God and profitable for reproof and instruction in righteousness, so the whole Bible remains profitable even while Pauline letters are emphasized.
Les teaches that for this age of grace, the Church Age, Paul is the designated Apostle of the Gentiles, so the Pauline letters provide the fundamental truths for salvation, the Christian walk, and the operation of the local church. Yet Les stresses this never implies the rest of the Bible is inappropriate. Paul himself writes that all Scripture is inspired of God and profitable for reproof and instruction in righteousness, and Romans is especially fundamental for Gentiles.