The Desperate Hardness of the Human Heart

In preparation for Maundy (Mandate) Thursday, I was reading from J.C. Ryle's Expository Thoughts on the Gospels: St. John. Regarding John 12:34-43, Ryle observed:

We err if we suppose that seeing wonderful things will ever convert souls. Thousands live and die this delusion. They fancy if they saw some miraculous sight, or witnessed some supernatural exercise of Divine grace, they would lay aside their doubts, and at once become decided Christians. It is a total mistake. Nothing short of a new heart and a new nature implanted in us by the Holy Ghost, will ever make us real disciples of Christ. Without this, a miracle might raise within us a little temporary excitement; but, the novelty once gone, we should find ourselves just as cold and unbelieving...