Once when he was to preach at the University of Sydney in Australia, John Stott lost his voice. He says:

What can you do with a missionary who has no voice? We had come to the last night of the [evangelistic campaign]. The students had booked the big university hall. A group of students gathered around me, and I asked them to pray as Paul did, that this thorn in the flesh might be taken from me. But we went on to pray that if it pleased God to keep me in weakness, I would rejoice in my infirmities in order that the power of Christ might rest upon me.

As it turned out, I had to get within one inch of the microphone just to croak the gospel. I was unable to use any inflection of voice to express my personality. It was just a croak in a monotone, and all the time we were crying to God that his power would be demonstrated in human weakness. Well, I can honestly say that there was a far greater response that night than any other night. I've been back to Australia ten times now, and on every occasion somebody has come up to me and said, "Do you remember that night when you lost your voice? I was converted that night."