Cats seemingly have no purpose. They just lounge all day, doing nothing. They have little impact on their surroundings. All they seem to do is entertain us and make our lives a little better.
Generally, the mission of animals is to make sure their genes survive by making sure they survive. They live because having one more specimen adds a little more chance to avoid extinction if something happens. It is essential for endangered species.
Back to cats, they have little effect outside their immediate surroundings. They hunt at nights, killing a few other animals that are unfortunate enough to cross their paths. But their reach is severely limited.
A cat does not care how many other cats are living in distant countries. Their life is not affected by them. As long as enough of them are living to ensure the survival of the species, they are localized.
But we, people, are not. Our reach is global, every single one of us. You can pick up the phone and call someone on the other side of the globe. Or send an email, or simply write something and put it on the Internet for everyone to see.
Imagine a line around the country you are living now. And then that all of a sudden, the world outside disappears completely. The cats around you wouldn't even notice. Even though their numbers shrunk by like 99%, that has little impact on their lives.
Not on yours. The result would be catastrophic. No more Internet, possibly no more electricity. The economy collapses, shortages and famine struck.
The point is, every human adds things to humanity as a whole. A few hundred years ago, it was less evident. But with trade, the effects still trickled to most parts of the world.
In the connected world, it a lot more apparent. When you write something on Facebook, it is there for everyone to see. If you order something online, do banking, or even when you consume electricity, you use global services. If nothing else, you provide data to some machine learning algorithms, so that recommendations will be more accurate for everyone.
You are not a cat and don't do like one. Make something valuable for everyone.
This is your purpose. To make the world a little better.