Innocent III was thirty seven when elected, a trained canon lawyer, and he understood the papal office as a jurisdiction rather than as an honour. His formulation of it was new and was quoted for centuries: the pope is set in the middle between God and man, below God and above man, less than God and more than man. Earlier popes had generally styled themselves vicar of Peter; he preferred vicar of Christ, and the change of title was a change of claim.
He used the instruments a canonist had. He placed France under interdict to force Philip Augustus to take back the wife he had repudiated, and did the same to England over a disputed appointment to Canterbury, holding out until John submitted in 1213 and received his kingdom back as a fief of the papacy. He intervened decisively in the contested imperial election, asserting the right to examine the fitness of a candidate for the empire.
He also had the judgement to recognise what was arriving. When Francis of Assisi came to Rome with a handful of companions and a rule of a few sentences, and when Dominic proposed an order of preachers, Innocent approved both, at a moment when unauthorised popular preaching was exactly what the church was suppressing elsewhere. The mendicant orders became the most effective religious institution of the following century, and the pope who might have crushed them did not.