John Piper writes: “My own serious consideration of fasting as a spiritual discipline began as a result of visiting Dr. Joon Gon Kim in Seoul, Korea. ‘Is it true,’ I asked him, ‘that you spent 40 days in fasting prior to the evangelism crusade in 1980?’ ‘Yes,’ he responded, ‘it is true.’”

Dr. Kim was chairman of the crusade expected to bring a million people to Yoido Plaza. But six months before the meeting the police informed him they were revoking their permission for the crusade. Korea at that time was in political turmoil and Seoul was under martial law. The officers decided they could not take the risk of having so many people together in one place. So Dr. Kim and some associates went to a prayer mountain and there spent 40 days before God in prayer and fasting for the crusade. Then they returned and made their way to the police station. “Oh,” said the officer when he saw Dr. Kim, “we have changed our mind and you can have your meeting!”

John Piper, A Hunger for God, (Crossway, 2013), pg. 65.