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. So, too, in the beginning many truths might have been proposed somewhat _obscurely_ or _less clearly_; they might have been _less urgently insisted upon_, because there was no heresy, no contrary teaching to render a more explicit declaration necessary. Now, a doctrine which is _implicitly, less clearly, not so earnestly_ proposed, may be overlooked, misunderstood, called in question; consequently, it may happen that some articles are now universally believed in the Church, in regard to which doubts and controversies existed in former ages, even within the bosom of the Church. “Those who err in belief do but serve to bring out more clearly the soundness of those who believe rightly. For there are many things which _lay hidden in the Scriptures_, and when heretics were cut off they vexed the Church of God with disputes; then the hidden things were _brought to light_, and the will of God was made known.” (St. Augustine on the 54th Psalm, No. 22.) This kind of _progress in faith_ we can and do admit; but the truth is not changed thereby. As Albertus Magnus says: “It would be more correct to style this the progress of the believer in the faith than of the faith in the believer.”