Comment by zdragnar
> What's the point of our existence if we have no way to meaningfully contribute to our own world?
You may find this to be insightful: https://meltingasphalt.com/a-nihilists-guide-to-meaning/
In short, "meaning" is a contextual perception, not a discrete quality, though the author suggests it can be quantified based on the number of contextual connections to other things with meaning. The more densely connected something is, the more meaningful it is; my wedding is meaningful to me because my family and my partners family are all celebrating it with me, but it was an entirely meaningless event to you.
Thus, the meaningfulness of our contributions remains unchanged, as the meaning behind them is not dependent upon the perspective of an external observer.
People talk about meaning, but they rarely define it.
Ultimately, "meaning" is a matter of "purpose", and purpose is a matter of having an end, or telos. The end of a thing is dependent on the nature of a thing. Thus, the telos of an oak tree is different from the telos of a squirrel which is different from that of a human being. The telos or end of a thing is a marker of the thing's fulfillment or actualization as the kind of thing it is. A thing's potentiality is structured and ordered toward its end. Actualization of that potential is good, the frustration of actualization is not.
As human beings, what is most essential to us is that we are rational and social animals. This is why we are miserable when we live lives that are contrary to reason, and why we need others to develop as human beings. The human drama, the human condition, is, in fact, our failure to live rationally, living beneath the dignity of a rational agent, and very often with knowledge of and assent to our irrational deeds. That is, in fact, the very definition of sin: to choose to act in a way one knows one should not. Mistakes aren't sins, even if they are per se evil, because to sin is to knowingly do what you should not (though a refusal to recognize a mistake or to pay for a recognized mistake would constitute a sin). This is why premeditated crimes are far worse than crimes of passion; the first entails a greater knowledge of what one is doing, while someone acting out of intemperance, while still intemperate and thus afflicted with vice, was acting out of impulse rather fully conscious intent.
So telos provides the objective ground for the "meaning" of acts. And as you may have noticed, implicitly, it provides the objective basis for morality. To be is synonymous with good, and actualization of potential means to be more fully.