He is famous for being a great preacher and reformer. He had a unique ability to project his voice and without the benefit of modern amplification he could be heard by up to 30,000 people in the open air. He was also responsible for instituting the feast of the Holy Name of Jesus for which he adopted (IHS).

He preached all over northern and central Italy, travelling everywhere on foot. He preached against the abuses of his day, including gambling and witchcraft. He urged the need for personal prayer and penance. He called for ethics in commerce to be based on peace and justice.

His voice and style were full of human warmth and joy. He could mimic and act, reducing his audience to tears or laughter as required. He was denounced for preaching false doctrine three times but on none of these occasions could the accusation be upheld. He may have been extreme in some ways but he was totally orthodox in his teaching and led a fine example by the way he lived his daily life.