God is generous and so he calls us to be as well. What we do with what God has given us shows the world where our hearts are at and helps proclaim the gospel. We want to glorify God with every area of our lives, and that includes what we do with our finances.
Each one must give as he has decided in his heart, not reluctantly or under compulsion, for God loves a cheerful giver.
2 Corinthians 9:7 (ESV)