More than anything, Carl Sagan understood how big the Universe really was- and how small we are in comparison. Some might expect that a true understanding of human significance would lead to nihilism- but Carl Sagan stands as proof that we can know our place in the Universe and realize that it means just the opposite.
We are small, we are tiny, and we are incredibly vulnerable in the darkness of space. There's so very few of us, and we're all in this together. Every life is so incredibly fragile, and so uncountably precious. For all we know, we really might be the only life in the Universe. Far more likely, there are other civilizations. In either case- there is only one Earth. There is only one planet that we know of where we can live. We need to take care of it, and each other.