She began to acquire a reputation as a person of insight and sound judgement, and many persons from all walks of life sought her spiritual advice, both in person and by letter. (We have a book containing about four hundred letters from her to bishops, kings, scholars, merchants, and obscure peasants.) She persuaded many priests who were living in luxury to give away their goods and to live simply.
In her day, the popes, officially Bishops of Rome, had been living for about seventy years, not at Rome but at Avignon in France, where they were under the political control of the King of France (the Avignon Papacy, sometimes called the Babylonian Captivity of the Papacy, began when Philip the Fair, King of France, captured Rome and the Pope in 1303). Catherine visited Avignon in 1376 and told Pope Gregory XI that he had no business to live away from Rome. He heeded her advice, and moved to Rome. She then acted as his ambassador to Florence, and was able to reconcile a quarrel between the Pope and the leaders of that city. She then retired to Sienna, where she wrote a book called the DIALOG, an account of her visions and other spiritual experiences, with advice on cultivating a life of prayer.
After Gregory's death in 1378, the Cardinals, mostly French, elected an Italian Pope, Urban VI, who on attaining office turned out to be arrogant and abrasive and tyrannical, and perhaps to have other faults as well. The Cardinals met again elsewhere, declared that the first election had been under duress from the Roman mob and therefore invalid, and elected a new Pope, Clement VII, who established his residence at Avignon. Catherine worked tirelessly, both to persuade Urban to mend his ways (her letters to him are respectful but severe and uncompromising -- as one historian has said, she perfected the art of kissing the Pope's feet while simultaneously twisting his arm), and to persuade others that the peace and unity of the Church required the recognition of Urban as lawful Pope. Despite her efforts, the Papal Schism continued until 1417. It greatly weakened the prestige of the Bishops of Rome, and thus helped to pave the way for the Protestant Reformation a century later.
Catherine is known (1) as a mystic, a contemplative who devoted herself to prayer, (2) as a humanitarian, a nurse who undertook to alleviate the suffering of the poor and the sick; (3) as an activist, a renewer of Church and society, who took a strong stand on the issues affecting society in her day, and who never hesitated (in the old Quaker phrase) "to speak truth to power"; (4) as an adviser and counselor, with a wide range of interests, who always made time for troubled and uncertain persons who told her their problems -- large and trivial, religious and secular.