Only a kind of childish narcissism permits the sincere belief that what matters to oneself just does, as such, matter-period. I have found that a very good measure of somebody's spiritual as well as emotional maturity is their ability to make that distinction and take it seriously. It is the capacity for that humility which expresses itself as critical distance—objectivity, if you like—and that in turn is prerequisite for all other spiritual growth. Even so, it would also be narcissistic to fashion an answer in the place where that fact seems to lead.
For what matters-period is what matters to God; so of course the question is answerable only from the God's-eye point of view. Most of us don't have that point of view even though some think we do, or at least think we ought to. The ethic of utilitarianism, for example, (which is nowadays more often called 'consequentialism' by philosophers, thanks to the late G.E.M. Anscombe) tells us that there are no actions which are absolutely forbidden or required; our moral duty is to do either that thing, or that sort of thing, whose overall consequences would in fact constitute a more optimal combination of good and bad than those of the alternatives would. Such a moral philosophy requires the agent, for all practical purposes, to strive to adopt the God's-eye point of view: a global, impersonal perspective from which one can make the necessary calculations. Now when the issue is purely practical—e.g., should a bridge be built over such-and-such river—we must strive to think in that fashion. When little of great moral or spiritual significance is at stake, we must make decisions in terms of the consequences we can envision for the various alternatives before us. But when the issue is one of bedrock moral principle, I think it should go without saying that such a perspective is impossible to attain by human power and that trying to attain it is not only delusory but destructive. To the extent it's taken seriously—and under various names or none at all, it is taken far more seriously by far more people than many seem imagine—such supposed pragmatism is absurdly narcissistic. It is the kind of narcissism that Satan showed in the guise of the serpent during the pre-history of the human race; it is the kind into which he seduced our first parents. Hence "the Fall." Evil is the price we pay for such pretense.
Yet I am inclined, by my reading and experience, to believe that some especially holy people are occasionally vouchsafed glimpses of spiritual reality from the God's-eye point of view. Even there, however, a distinction must be made to forestall confusion. Divine revelation gives us a general answer to the question what matters to God: what matters to God, vis-à-vis humans at least, is how well we love, which is to say how much we allow ourselves to be moved by his grace. So, in the individual life of the Christian, what "matters, period" is how well they love in the concrete circumstances in which they find themselves. Sometimes it is fairly clear, if not morally certain, that one has done so or failed to do so. So in that respect, it is sometimes clear what matters-period; indeed, one's efforts through prayer, self-denial, and study to become a person more likely to love God and other people as God wills also matter-period. But even granted that, much remains far from clear.
For if we leave things at that, a great deal of what we do seems to serve at best only as raw material for what matters-period. It does not matter-period in itself and doesn't even seem meant to be. Most people, for instance, spend most of their time earning a living, eating, sleeping, and in general attending to the myriad, often-boring tasks of maintaining physical existence and health. Aside from that, much time seems to be spent on entertainment when we're too tired, disgusted, or ill-disciplined to do much of anything else. Only a fortunate minority get to earn a living by doing something they truly care about; much of what the majority, to which I belong, does seems to matter only as a means to other things, about which one can then raise the same questions. Yet treating such instrumental actions and goods merely as a means to other ends undermines one's capacity to do them well, as they must be done if our existence is not to descend into chaos, sickness, and poverty. I know for my own part that I do much of what I do not for its own sake, or even because I believe it will lead to something that "matters-period," but simply so as to avoid the unpleasant consequences of not doing it. And much the same could be said of countless other people. What "matters-period" about that? Clearly, the motivation for doing them comes from the fact that, for obvious reasons, they matter to us as kinds of negative means to ends we cannot help caring about. But that doesn't answer the question whether, or even how, they matter-period.
I think there should be an answer to that question. I do not believe that God made some things purely as means, whether constitutive or instrumental, positive or negative, to other things. And I believe there is an answer to that question. It's not simple or obvious and certainly can't be developed cogently in a blog post. That's one reason why I invite readers to offer their suggestions. But I can close with this much: if we offer such raw material to God to do with as he wills, he will do something with it that matters-period just because he's doing it.