Years ago at USC, there was a professor of philosophy teaching there who was a deeply committed atheist. His primary goal for one required class was to spend the entire semester attempting to prove that God couldn't exist.
His students were always afraid to argue with him because of his impeccable logic. For twenty years, he had taught this class and no one had ever had the courage to go against him. Sure, some had argued in class at times, but no one had ever really gone against him because of his reputation. At the end of every semester on the last day, he would say to his class of 300 students. "If there is anyone here who still believes in Jesus , stand up!" In twenty years, no one had ever stood up. They knew what he was going to do next. He would say, "Because anyone who believes in God is a fool. If God existed, he could stop this piece of chalk from hitting the ground and breaking. Such a simple task to prove that He is God, and yet He can't do it." And every year, he would drop the chalk onto the tile floor of the classroom and it would shatter into a hundred pieces. All of the students would do nothing but stop and stare. Most of the students thought that God couldn't exist. Certainly, a number of Christians had slipped through, but for 20 years, they had been too afraid to stand up.
Well, a few years ago there was freshman who happened to enroll. He was a Christian, and had heard the stories about his professor. He was required to take the class for his major, and he was afraid. For three months that semester, he prayed every morning that he would have the courage to stand up no matter what the professor said, or what the class thought. Nothing they said could ever shatter his faith - he hoped. Finally, the day came. The professor said, "If there is anyone here who still believes in God, stand up." The professor and the class of 300 people looked at him, shocked, as he stood up at the back of the classroom. The professor shouted, "You FOOL!" If God existed, he would keep this piece of chalk from breaking when it hit the ground!" He proceeded to drop the chalk, but as he did, it slipped out of his fingers, off his shirt cuff, onto the pleat of his pants, down his leg, and off his shoe. As it hit the ground, it simply rolled away unbroken. The professor's jaw dropped as he stared at the chalk. He looked up at the young man, and then ran out of the lecture hall. The young man who had stood, proceeded to walk to the front of the room and shared his faith in Jesus for the next half hour. 300 students stayed and listed as he told of God's love for them and of His power through Jesus.