We give because God is generous to us, we give because he gave his only son to be poor, so we could be rich in him. God’s people should be a generous people.
Since God has redeemed us, he has claim on us. We no longer seek our own desires, but the good of others and the glory of God.
In our culture of self-appeasement, it is hard to imagine giving all of ourselves for Christ's sake, and yet he poured himself out for us, dying a death we should have died, all so we could have life to the fullest.
On the cross, we see both the perfect love and perfect judgment, as God's wrath is poured out on Jesus for our sake.