You can mine lunar platinum, for example. That can be used for fuel cells on Earth. You can make solar power satellites and launch them from the moon into Earth orbit. From there it can provide energy to the Earth.
It takes less energy to get from the Moon to Earth orbit, so it will be more economical.
Hydrogen can be obtained from seawater and made into methanol and shipped to wherever it is needed. Methanol can be electrolyzed back into hydrogen, while saving the carbon dioxide, making it carbon neutral.
The solar power satellites and the platinum can sustain a lunar colony, which saves the expense of getting there because someone is already there. Their being there has to be sustained and the reason for being there will be sustained because there are resources on the moon which can be exploited. The economic activity can expand further into deeper space, yielding additional returns.
You can also fashion new worlds from lunar materials. Getting to and from an Earth Moon Lagragian point to another point in space is a lot easier and cheaper than launching rockets from the ground- even if launch costs come way down. Space exploration and settlement becomes all the more economically feasible and profitable. This will yield benefits on the ground, making everyone better off.