Attachment to earthly things isn't healthy. We use money to buy our necessities, but we also squander it on trivial things- designer clothes, bigger TVs, smaller phones, etc. In doing so- while we support the livelihoods of the people who make these things- we ignore the least of us. We ignore Jesus when we spoil ourselves, and so we ignore the duties He has entrusted us with.
There's two reasons (that I can think of) that we are called to care for the poor. Chiefly, we carry out Jesus' charge to care for the least among us. We shouldn't neglect those who are in need. It's against the human person to ignore them in their distress, and while we (one person) can't give to all, we must give to who we can. It satisfies their physical needs, and lets our lights shine.
Second, in doing these things, we build up for ourselves spiritual treasure in heaven- where moth doesn't eat and thieves don't steal what we have made for ourselves. In other words, it's for our own spiritual wellbeing that we do those things. In losing our earthly possessions for such a noble cause, we gain in heavenly "possessions". James tells us that our faith is dead if we give someone a blessing without giving them a coat (I'm paraphrasing), so let's build up our fellow man and build up for ourselves a delightful eternity.