We are all poor.
One simple reason we should all have solidarity with the poor is that, in the grand scheme, we are all poor. We do not make ourselves. We receive our very existence and the universe we exist in as a gift. Anything we earn or do is laid on that foundation. We do not sustain ourselves, no matter how productive or independent we are. Even if we grew all our own food, and made all of our own clothing and shelter, we would depend on the soil, trees, rocks and animals. We would use our hands and minds given to us by our parents and our Maker. Finally, no matter how many earthly goods or honors we aquire, we are destined to lose them all. At the end, we lay them all aside. Whatever life is about, it can't just be about piling that stuff up. We are all poor. Some of us just don't know it yet. Including me (most of the time.)