In the first three centuries of Catholic Church history, there was no law prohibiting the ordination of married men, and many priests were married. But marriage was never permitted after ordination. Moreover, all the Priests whether married, single, or widowed practiced sexual abstinence after ordination.
The first recorded Church legislation concerning clerical celibacy in the West was decreed at the Synod of Elvira in Spain around the year 300, and in 385, Pope Siricius (384-399) authorized celibacy for all clergy in the West.
But despite the longstanding practice of the Church, priests in the early medieval Church often did not live celibacy faithfully. Many priests were not trained or formed properly, and they turned down their vow of celibacy, taking mistresses and concubines who bore them children, causing too much scandal in the Church. Some of the priests engaged in homosexual acts. All the while, bishops and abbots seemed hesitant to act and bring virtue to the priesthood and monasteries.
But one monk named Peter Damain was not scared to fight the immoralities going on the Church, and he wrote a book in which he called for Leo IX to remove this stain of clerical immorality.
Peter was ordained a bishop but was later created a cardinal. Peter wrote plenty letters, sometimes he signs them as “Peter the Sinner” or “Peter the Sinner-Monk,” which brought a window into the soul of this important saint in the life of the Church. The life of St. Peter Damian is a model of virtue to Catholic priests, and his words provide advice and a warning for all Catholics not to let sexual vice contaminate the life and mission of the Church.