Why does Paul reveal things the rest of Scripture doesn't touch on?
Paul reveals things the rest of Scripture doesn't touch on because it is in his writings alone that the true nature of the old Adam—the inherited Adamic sin nature—is made known. The Old Testament and Jesus taught the heart is wicked, but Paul alone explains this inherited sin nature from Adam, and he clarifies the resurrection order in 1 Corinthians 15.
Les explains that John 5:28-29 seems to teach a general resurrection where the saved and lost rise at the same time. But when you come back to 1 Corinthians 15, Paul reveals that there are two distinct groups and resurrections. That is why Paul is the one who reveals so many things the rest of Scripture doesn't even touch on. Les also notes that many today ignore Paul's epistles, yet it is in Paul alone that we find the true nature of the old Adam. While the Old Testament says the heart is desperately wicked, and Jesus taught the heart was wicked, it isn't until Paul's writing that we understand this Adamic sin nature is inherited ever since Adam.