In We Shall See God, I share a remarkable story that Spurgeon told about an experience early in his ministry:
In 1857, a day or two before preaching at the Crystal Palace, I went to decide where the platform should be fixed; and, in order to test the acoustic properties of the building, cried in a loud voice, “Behold the Lamb of God, which taketh away the sin of the world.” In one of the galleries, a workman, who knew nothing of what was being done, heard the words, and they came like a message from heaven to his soul. He was smitten with conviction on account of sin, put down his tools, went home, and there, after a season of spiritual struggling, found peace and life by beholding the Lamb of God.
It was on his deathbed that this man told the story of his conversion, the result of God speaking to him through a single verse of Scripture uttered by Spurgeon. When Spurgeon preached in that building a day or two later, it was to a crowd of 23,654 people. But such is the power of Christ, the Lamb of God, who takes away the sin not only of the world, not only of a potential 23,654 people, but of one lone man working in a building when a preacher came to test the acoustics. This man will be forever grateful that when Spurgeon stood up front to do a sound check, he did not simply count to ten!