The hardest parts of Scripture, in my experience, are not the bits you don't understand. Failing to understand can be good; it can prompt thought, investigation, and discovery. No, the real trouble comes when you know exactly what is going on, and it doesn't look good, true, or beautiful. Think, for instance, of the prophetic oracles of judgment against the nations, which run for page after terrifying page, with (apparently) no hope, no contemporary application, and no end in sight.