There are certain disciplines, cultural practices and pastoral considerations of the Catholic Church that can and sometimes do change over time. The doctrines of the Church, however, cannot change. Truth does not become untruth.
The Apostles handed down (Tradition) that which was given to them by Christ. Some of it was written down, some of it was spoken and some of it was implicit (which is why an exhaustive list of the deposit of faith cannot be written down). The Holy Spirit guides the Church into all truth as promised by Christ. This means that the understanding of some doctrine develops over time.
The Church has the authority to be God’s “mail carrier.” In other words, the Church is tasked with the responsibility of delivering to the world God’s truth as given by Christ. The Church is not authorized to “edit God’s mail.” The Church cannot change the doctrine contained within the deposit of faith. Doctrines delivered to the world cannot be reversed or declared “no longer true.” In this respect, the Catholic Church claims less authority than Protestant churches.
Prior to 1930, all churches taught that artificial birth control is immoral. Today, the Catholic Church stands alone in teaching this truth. Even when many individual Catholics fail to obey the doctrine, the Church does not reverse the truth of the doctrine. That which is immoral does not become moral simply because society changes its views. Truth is not determined by vote.
Jesus Christ taught that divorce is wrong because it defies the bond that God designed between man and woman “from the beginning.” Unlike Protestant churches, the Catholic Church does not claim to have the authority to change this doctrine of Christ and allow divorce. Additionally, the Catholic Church cannot change the fact that God designed marriage to be between one man and one woman. Some Protestant churches claim the authority to alter God’s design for marriage. Nevertheless, authentic development of doctrine cannot declare a previously held truth “untrue.”
Jesus Christ ordained men to carry out certain priestly duties within the Church. The Catholic Church does not have the authority to ordain priestesses. This is not the patriarchal oppression of women or the “invention” of a New Testament priesthood under Constantine. It is part of the deposit of faith handed down by the Apostles.
The Catholic Church infallibly declared the canon of the Bible in the 300s. This reality stands to reason if one is to regard the Bible as infallible. As Dr. Peter Kreeft has said, “How can you squeeze infallible Bible ‘juice’ out of a fallible Catholic Church ‘orange’? The effect cannot be greater than its cause.” Protestantism removed some books from the canon of Scripture by its own authority in the 1500s. It declared “untrue” that which had already been declared true. If Martin Luther is a fallible man, how can anyone trust that his canon of Scripture is infallible? By reversing that which had already been declared true, Martin Luther, along with other reformers, claimed more infallible authority than even the Catholic Church.