Given our abundance, the burden of proof should always be on keeping, not giving. Why would you not give? We err by beginning with the assumption that we should keep or spend the money God entrusts to us. Giving should be the default choice. Unless there is a compelling reason to spend it or keep it, we should give it.
God comes right out and tells us why he gives us more money than we need. It's not so we can find more ways to spend it. It's not so we can indulge ourselves and spoil our children. It's not so we can insulate ourselves from needing God's provision. It's so we can give and give generously (2 Corinthians 8: 14; 9: 11)
Giving up everything must mean giving over everything to kingdom purposes, surrendering everything to further the one central cause, loosening our grip on everything. For some of us, this may mean ridding ourselves of most of our possessions. But for all of us it should mean dedicating everything we retain to further the kingdom. (For true disciples, however, it cannot mean hoarding or using kingdom assets self-indulgently.)
It's curious that the Church has become the most tightfisted at the very time in history when God has provided most generously. There's considerable talk about the end of the age, and many people seem to believe that Christ will return in their lifetime. But why is it that expecting Christ's return hasn't radically influenced our giving? Why is it that people who believe in the soon return of Christ are so quick to build their own financial empires--which prophecy tells us will perish--and so slow to build God's kingdom?