Giving is a part of our worship to God. Not only that, but God influences the world through His people. He gives to us so that He can give through us. The Bible tells us that everything we have is a gift from God (1 Chronicles 29:14). As you give both faithfully and willingly, the world is changed for the glory of God: the gospel is preached and lives are changed.
"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)