Credere voluntatis est, to believe depends upon the free will, says St.Thomas (II-II:10:8), and the minister of baptism, before administering the sacrament, is obliged to ask the question, "Wilt thou be baptized "?Usually all priests exercising the sacred ministry receive faculties for reconciling heretics.When conditional baptism is administered, sacramental confession is also required from the convert. Augustine.) In the Middle Ages the word conversion was often used in the sense of forsaking the world to enter the religious state. More commonly do we speak of the conversion of an infidel to the true religion, and most commonly of the conversion of a schismatic or heretic to the Catholic Church.
In the Latin Vulgate ( Acts 15:3 ), in patristic (St. Dei, VIII, xxiv), and in later ecclesiastical Latin, conversion refers to a moral change, a turning or returning to God and to the true religion, in which sense it has passed into our modern languages. Every man is bound by the natural law to seek the true religion, embrace it when found, and conform his life to its principles and precepts.And since faith is necessary for salvation, that we may comply with the duty of embracing the true Faith and persevering in it, God by His only-begotten Son has instituted the Church and has adorned it with obvious marks so that it may be known by all men as the guardian and teacher of revealed truth.These marks (or notes) of credibility belong to the Catholic Church alone. The first step, therefore, in the normal process of conversion is the investigation and examination of the credentials of the Church, which often is a painful labor lasting for years.For many of the truths of revelation, being mysteries, are to some extent obscure.Yet, it is not a blind act, since the fact that God has spoken is not merely probable but certain.