It is not ours, even if we hold title to property. God has mearly lent it to us for our earthly use. Such is the meaning of those magnificent words in the Union Prayer Book, reminding us that all that we have and prize is but lent to us and we are but stewards of whatever we possess. We must share a portion of what God has lent us with those who have less. Such is the reason for the obligation of tzedakah .
Charity is a poor translation, because charity is something voluntary.
Tzedakah is mandatory. It makes us outer-directed. It enjoins us to do good for others. Thus, when God blesses us with material abundance, God also mandates us to part with a portion of it to better the lives of those stricken with hunger and privation. Our commentators expand upon the meaning of this verse.