The church believed that the Earth was the center of the universe and the sun and the other planets revolved around the Earth. On the other hand, Galileo believed that the Sun was the center of the universe and the planets revolved around the Sun. The church made Galileo stand at a meeting to say that the Earth was at the center of the universe. He said that, but muttered under his breath, "The sun is the center of the universe." Or something like that. The church was mad at Galileo for not believing what the church believed, so they arrested him.
He was charged with heresy for going against the teachings of the church. He said that the planets revolved around the Sun when the church said the Earth was the center of the universe, (they had no idea that ours is just a solar system and not the entire universe.)