Richard Sibbes, one of the great old Puritan preachers of Cambridge who died in 1635, wrote a whole book (175 pages) on Psalm 42:5. He was called “the sweet dropper” because of how much confidence and joy his sermons caused. He called his book The Soul’s Conflict with Itself, because in Psalm 42:5 that is exactly what you have, the soul arguing with itself, preaching to itself. “Why are you cast down, O my soul, and why are you disquieted within me? Hope in God!”
John Piper