NASA is humanity's gateway to the wider universe, our means of knowing what is out there beyond our planet 'Earth'.
Why do we bother trying to find out what is there? Because Humankind are curious of the unknown. Discovering what lies beyond the unknown is a common goal that unites humanity.
Another reason NASA is so greatly important is that, sooner or later our planet, as great as it is, will be gone or uninhabitable, or reaped of all necessary resources. I'm sure you've heard the phrase
"Only when the last tree has died and the last river been poisoned and the last fish been caught will we realize we cannot eat money"
This saying is so fitting because so much budget goes to "Defense" and relatively so little to NASA. It's time to rethink our priorities. Explore, not War.