She was elected prioress in the first month of the year 1552. Her immediate duty was to instruct her sisters, and to inspire them with an appreciation of their sublime vocation. Often she called her community to the chapter-room, and, addressing to them a doctrine which came from God himself, she taught her spiritual daughters the way they were to follow in order to reach the summit of religious perfection. She has left us an abridgment of her mystical teaching in a letter which she addressed to a religious. "At first," says she, "we must endeavor to be disengaged from every earthly affection, loving no creature but for God's sake; then, advancing a degree, we must love God, not only from self-interest, but purely for himself and because of his supreme excellence.
"Secondly, all our thoughts, words, and actions should tend towards God; and by our prayers, exhortations, and good example, we should aim only at procuring his glory in ourselves and in others.
"Thirdly, and lastly, we should rise still higher in the fulfilment of God's will, to such a degree as to have no longer any desire in regard to the misfortunes or joys which happen to us in this miserable life.
"But we shall never arrive at this height of perfection unless by a firm and courageous denial of our own will. To acquire such self-abnegation, it is absolutely necessary to lay the foundation of profound humility, that, by a perfect knowledge of our own misery and fragility, we may ascend to the knowledge of the greatness and goodness of our God."
It appears that the whole spiritual doctrine of S. Catharine is contained in these two fundamental points—self-abnegation and humility, in order to deserve the enjoyment of divine contemplation: this is the true and the only way to sanctity.
Although the first duty of a superior is to guide those confided to his care, he has, however, a more painful task—he must govern them; and it is here that the superior meets the most serious obstacles in the exercise of his charge. It is always difficult to govern others; for government is the application of laws with firmness, yet without too much severity. Now, human nature shrinks from submission, which, nevertheless, the superior is obliged to require, unless he be a prevaricator; on the other side, he must often adopt measures of government which can be discerned only by the most consummate prudence and a profound knowledge of the weakness of human nature.
In a religious community the difficulty is still greater; for the law is supported by conscience only, and it tends to guide those who have accepted it to that ideal perfection in which the soul is no longer attached to the earth. During forty years S. Catharine governed the convent of Prato with a prudence, a sweetness, and a firmness that made it the perfect type of a religious community. She combated most energetically all abusive exemptions from common life, and showed herself a faithful guardian of holy observances. But if she was the enemy of relaxation of the rule, she also censured severely the proud zeal of those souls whose whole perfection consisted in repeating the prayer of the Pharisee: "O God, I thank you that I am not as the rest of men. I fast twice a week."
Under the direction of a prioress so holy and so wise, the Sisters of Prato walked with rapid strides in the way of perfection; and how could it be otherwise, when they beheld their superioress tender towards them as a mother, and discharging her offices sometimes even in the raptures produced by the divine revelations?
The influence of S. Catharine was not confined to the monastery of Prato. God would not permit that this community should be the only witness of such elevated sanctity. The religious of her order—her brethren in S. Dominic—were the first witnesses of the extraordinary graces which she had received from heaven, and, on her side, S. Catharine had for them the greatest esteem, the most lively affection, regarding them as laborers chosen by God to cultivate his choicest vineyard. Every time the fathers came to Prato to exercise the functions of prior, confessor, or preacher, they seemed to her as "so many angels descended from heaven, whose presence alone was sufficient to inspire the sisters with sentiments of respect, and whose coming was to infuse fresh zeal for a more perfect life."
By degrees the influence of S. Catharine, and the renown of her sanctity, were spread throughout Italy. Persons from all parts came to consult her and beg her prayers. Joan of Austria, Archduchess of Tuscany, was bound to her by a tender friendship; she went often to the convent of Prato to confide to the holy prioress all the vexations and sorrows of her life. She profited so well by the counsels of her holy friend that she was no longer called by other name than the good archduchess. As if Germany envied Italy the treasure she possessed in the monastery of Prato, the King of Bavaria sent his son there to convince himself of that which the renown had spread concerning this servant of God, and to recommend himself and his kingdom to her prayers. The influence of S. Catharine in the world had been deepest on those whom the author of her life so justly calls her spiritual sons: Antonio de Gondi, Philippo Salviati, Giovanni-Batisti de Servi, Lorenzo Strozzi, and many others.