Hence, whenever it has been defined that any point of doctrine pertained to the Catholic faith, it was always understood that this was equivalent to the declaration that the doctrine in question had been revealed to the Apostles, and had come down to us from them, either by Scripture or tradition. And as the acts of all the Councils, and the history of every definition of faith evidently show, it was never contended that a _new revelation_ had been made, but every inquiry was directed to this one point--whether the doctrine in question was contained in the Sacred Scriptures or in the Apostolic traditions.
A revealed truth frequently has a very extensive scope, and is directed against error under its many changing forms. Nor is it necessary that those who receive this revelation in the first instance should be explicitly acquainted with its full import, or cognizant of all its bearings. Truth never changes; it is the same now, yesterday, and forever, _in itself_; but our relations towards truth may change, for that which is hidden from us today may become known to us tomorrow. "It often happens," says St. Augustine, "that when it becomes necessary to defend certain points of Catholic doctrine against the insidious attacks of heretics they are more carefully studied, they become _more clearly understood_, they are _more earnestly inculcated_; and so the very questions raised by heretics give occasion to a more thorough knowledge of the subject in question."(29)
Let us illustrate this. In the Apostolic revelation and preaching some truths might have been contained _implicitly_, _e.g._, in the doctrine that grace is necessary for every salutary work, it is implicitly asserted that the assistance of grace is required for the inception of every good and salutary work. This was denied by the semi-Pelagians, and their error was condemned by an explicit definition. And so in other matters, as the rising controversies or new errors gave occasion for it, there were more _explicit_ declarations of what was formerly _implicitly_ believed. In the doctrine of the supreme power of Peter, as the visible foundation of the Church, we have the _implied_ assertion of many rights and duties which belong to the centre of unity. In the revelation of the super-eminent dignity and purity of the Blessed Virgin there is implied her exemption from original sin, etc., etc.