Impressions

 Now, here I observe, first of all, that, naturally as the inward idea of divine truth, such as has been described, passes into explicit form by the activity of our reflective powers, still such an actual delineation is not essential to its genuineness and perfection. A peasant may have such a true impression, yet be unable to give any intelligible account of it, as will easily be understood. But what is remarkable at first sight is this, that there is good reason for saying that the impression made upon the mind need not even be recognized by the parties possessing it. It is no proof that persons are not possessed, because they are not conscious, of an idea....

......Now, it is important to insist on this circumstance, because it suggests the reality and permanence of inward knowledge, as distinct from explicit confession. The absence, or partial absence, or incompleteness of dogmatic statements is no proof of the absence of impressions or implicit judgments, in the mind of the Church. Even centuries might pass without the formal expression of a truth, which had been all along the secret life of millions of faithful souls. 

This, from Newman's  sermon The Theory of developments in  Doctrine, is helpful in answering my questions from Development and Illumination.   I haven't read all the way through it yet, but he contrasts in quite a bit of detail the early Church, where many people including the Church Fathers could write unsystematically but faithfully about divine things that hadn't yet been challenged by heresies,  and today, when we have more scientific language about truths of the Faith than was necessary then.

His main point is that the formulations are made in reference to a Reality, in fact, that they have a Divine Object.   

The Apostle said to the Athenians, "Whom ye ignorantly worship, Him declare I unto you;" and the mind which is habituated to the thought of God, of Christ, of the Holy Spirit, naturally turns, as I have said, with a devout curiosity to the contemplation of the Object of its adoration, and begins to form statements concerning Him before it knows whither, or how far, it will be carried. One proposition necessarily leads to another, and a second to a third; then some limitation is required; and the combination of these opposites occasions some fresh evolutions from the original idea, which indeed can never be said to be entirely exhausted. This process is its development, and results in a series, or rather body of dogmatic statements, till what was at first an impression on the Imagination has become a system or creed in the Reason.

Now such impressions are obviously individual and complete above other theological ideas, because they are the impressions of Objects. Ideas and their developments are commonly not identical, the development being but the carrying out of the idea into its consequences. Thus the doctrine of Penance may be called a development of the doctrine of Baptism, yet still is a distinct doctrine; whereas the developments in the doctrines of the Holy Trinity and the Incarnation are mere portions of the original impression, and modes of representing it. ....

Doctrinal propositions express truth but can't exhaust the reality: 

 Particular propositions, then, which are used to express portions of the great idea vouchsafed to us, can never really be confused with the idea itself which all such propositions taken together can but reach, and cannot exceed. As definitions are not intended to go beyond their subject, but to be adequate to it, so the dogmatic statements of the Divine Nature used in our confessions, however multiplied, cannot say more than is implied in the original idea, considered in its completeness, without the risk of heresy. Creeds and dogmas live in the one idea which they are designed to express, and which alone is substantive; and are necessary only because the human mind cannot reflect upon that idea, except piecemeal, cannot use it in its oneness and entireness, nor without resolving it into a series of aspects and relations. And in matter of fact these expressions are never equivalent to it; we are able, indeed, to define the creations of our own minds, for they are what we make them and nothing else; but it were as easy to create what is real as to define it; and thus the Catholic dogmas are, after all, but symbols of a Divine fact, which, far from being compassed by those very propositions, would not be exhausted, nor fathomed, by a thousand.

Heretics draw false conclusions, often by over-emphasizing one doctrinal aspect, which ends up misrepresenting the Reality beyond the various doctrines.    This is why simple devout folk are often more conscious of heresy, and more attuned to the reality of Divine things,  than the professionals (or the unrepentant sinners whose minds are clouded by the effects of the ongoing sin) , because these simple folk have what Newman calls an Impression of the real thing that doesn't match the false emphasis of the heretics. 

Newman talks about how people receive religious impressions -- by impressions he does not mean intuitions or influences aside from real things -- he means impression in the sense that a seal molds wax and makes it into a similitude of itself, I think.   This is an account for how relatively uneducated people can know Truth -- one thinks of saints such as St Faustina Kowalski, or St Therese of Lisieux, or St Catherine of Siena.   His first means are a kind of gratuitous inspiration, and the effects of baptism, and he goes on:  

The secondary and intelligible means by which we receive the impression of Divine Verities, are, for instance, the habitual and devout perusal of Scripture, which gradually acts upon the mind; again, the gradual influence of intercourse with those who are in themselves in possession of the sacred ideas; again, the study of Dogmatic Theology, which is our present subject; again, a continual round of devotion; or again, sometimes, in minds both fitly disposed and apprehensive, the almost instantaneous operation of a keen faith.

By apprehensive I don't think he means anxious; I think he means inclined towards apprehending the reality of Divine things. 

 Throughout the sermon he parallels the development of understanding in the individual person --  exemplified perfectly by Mary -- with the development of understanding in the Church.