Sabbath and Jubilee Years

Part of today's reading is comforting in how it shows again how easily God provides for his people. We know how in the dessert God provided water, manna, and quail to the Israelites. I posted previously about how God is also watching out for his people as well by withholding problems. Today we see him commanding Sabbath and Jubilee years where no work was to be done, and he promised to take care of them one or two years in a row by providing them an abundance in the preceding year. It's a simple thing for God. He will take care of us without a second thought. Why is it so hard, then, for us to give abundantly to God and others?