As long as our only home is the planet Earth, our fate is tied to its fate. We can be utterly destroyed by any of numerous planetary catastrophes, such as nearby supernovae, giant solar flares, a large asteroid or comet impact, even a supervolcano or flood basalt eruption. On a longer timeframe, we know that our sun will someday expand into a red giant, likely vaporizing the Earth.
To have a future, we must expand into space, and ultimately to other stars as well.
People talk about building colonies on the moon or Mars. Some talk about outposts on Venus or Mercury, or even of terraforming Mars and/or Venus to make them suitable for human habitation. I don't see it.
The reason it doesn't make sense to inhabit the planets around our sun, or around other suns, is that they are at the bottom of gravity wells. It takes a huge expenditure of energy to get into space from a planetary surface, energy lost when you land there. It takes about as much energy to get into Earth orbit as it takes to get to the asteroid belt from Earth orbit. In other words, in a hundred-million mile trip to the asteroid belt, half of the energy is used going the first thousand miles.
An asteroid, on the other hand, has very little gravity, even one several miles across. To travel from one asteroid to another takes time, but relatively little energy. Most asteroids appear to be carbonaceous, meaning that they contain large amounts of the volatiles we need to thrive and expand: water, hydrocarbons, nitrogen compounds. They also contain vast quantities of iron and other metals. And the resources of as asteroid are easy to reach: we can mine the entire body, even one miles thick. On the Earth, on the other hand, we must be content with scratching the surface. Between heat and crushing pressure, we can only tap the outer mile or so (and usually much less).
Together, all of the asteroids mass only about one hundredth of the Earth, yet the availability of those asteroidal resources is such that they could support a population a hundred times greater than the Earth.
We need to move into space for humanity to have a future. And the logical places to colonize first are not planetary surfaces, but the millions of available asteroids.