He went later to Salamanca to study, and there being taken into the celebrated College of St. Bartholomew, he did his priestly office, so that he was at once constant to the studies he desired and busy with sermons. Here he had a severe illness, and vowed to take up a sterner way of living. In fulfilment of this vow, he gave to an half-naked beggar the better of the two garments which were all that he had, and then went to a Convent of the friars of St. Augustine, which was then in the richest bloom of rigid discipline. Being admitted therein, he surpassed the most advanced in obedience, lowliness, watchings, and prayer. At the time that he had charge of the table, one keg of wine abundantly sufficed in his hands for all the friars, throughout an whole year. After his year of noviceship, he undertook the duty of preacher at the command of his Superior. At that time, owing to bloody feuds, all things human and divine at Salamanca were in such utter confusion, that murders were committed almost every hour, and the streets and squares, and the very churches, flowed with the blood of all classes, especially of the nobility.
It was John, who by public preaching and private conversations, softened the hearts of the citizens so that the town was restored to peace. He grievously offended one of the nobles by rebuking him for his cruelty towards his vassals. This man sent two knights to murder him on the road. They had already come nigh him when God sent a terror upon them, so that they and their horses stood still, until they cast themselves down before the feet of the Saint, imploring his forgiveness for their sin. The Prince himself, also, smitten with a sudden dread, despaired of his salvation, till he had sent for John, who, finding him repent of his deed, restored him to soundness. Some quarrelsome men, likewise, who were reluctant to give him a beating with a cudgel, found their arms stiffen, nor would their strength come back till they had asked his pardon for their wickedness. Oftentimes when he was celebrating the Holy Liturgy, the Presence of the Lord Christ became sensibly manifest to him, and he drank in things heavenly from their Divine Well-head himself. Oftentimes also he could see the secrets of men's hearts, and foretell strange things to come. He raised from the dead his own niece, aged seven years. He foretold the day of his own death, and prepared himself by receiving most devoutly the Sacraments of the Church. God glorified him by many miracles, both before and after his death. These being duly proved, Alexander VIII numbered him among the Saints.