What does it mean for something to "matter" anyway? Does interacting with the world mean that your beliefs now matter? What if your brain-in-a-vat was hooked up

What does it mean for something to "matter" anyway? Does interacting with the world mean that your beliefs now matter? What if your brain-in-a-vat was hooked up to a computer that would encode your synapses on paper on the other side of the world? Does that "matter"? Not trolling, just trying to make sense of what you mean by your sentence.