Endowed with apostolic virtues and passion, after the premature death of his younger brother Federico, he passed through a hard religious crisis between 1562 and 1563. Although he was extremely rich and soul inheritor of his father’s wealth, the young Cardinal pursued perfection and sanctity rigorously. He fasted and prayed long hours, eating bread and water one day per week.

When he was 27 years old, he was nominated Milan Archbishop. There he consecrated himself a tireless pastor and went through rough pathways. He initiated his residence in the Diocese with much generosity and unselfishness. He renounced functions and his wealth. The lay historian Francesco Cusani wrote in 1861: "Carlo started as a beautiful example of unselfishness and renounced an annual income of one million and three hundred liras from the feud, benefits and pensions donated by the Pope. He used this amount for public benefit and applied part of it to build useful and great deeds".

He used to do frequent peregrinations especially to Our Lady Sanctuaries. On his trips and apostolic activities he left vestiges of his sanctity and Good News announcements. He distinguished himself in founding 740 catechist schools attended by more than 40.000 people, oriented by 2000 lay catechists he taught.

He intervened on his epoch social life. With his ability and wisdom, he introduced changes and fought against power injustice against humbles. St. Charles took part on Council of Trento and his ideas were well received and turned into our Church Heritage.

Historically, his image is related to the innumerous social works organized in Milan by the time of the hard famine in 1570, and also by the time of the terrible plague between 1576 and 1577 which until today is known as "St. Charles Plague".

He was canonized on November 1, 1610.

St. Charles is a model of patience, constancy, charity and apostolic passion. He was chosen by John Baptist Scalabrini as patron and protector of the missionary congregations of the Sisters and Fathers he founded.