In his rebuttal to the objection that, since it's lawful to own things, it's lawful not to give alms, St. Thomas quotes an interesting perspective from St. Basil the Great:
Why are you rich while another is poor, unless it be that you may have the merit of a good stewardship, and he the reward of patience?
See, if everybody sold all he had and gave the money to the poor, then no one would be left to be a good steward, and creation would fail to express the good stewardship aspect of God.