25 They can, it is true, be made clearer and more obvious; and doing this is of great benefit. But it must always be done in such a way that they retain the meaning in which they have been used, so that with the advance of an understanding of the faith, the truth of faith will remain unchanged. For it is the teaching of the First Vatican Council that "the meaning that Holy Mother the Church has once declared, is to be retained forever, and no pretext of deeper understanding ever justifies any deviation from that meaning." (11)
Source: Mysterium Fidei (Vatican.va)