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.
2 Corinthians 9:7: "Let each one give [thoughtfully and definitely] just as he has purposed in his heart, not grudgingly or sorrowfully or under compulsion, for God loves [Whose heart is in His work] a cheerful and joyous giver [whose heart is in his giving]."
Malachi 3:10: "Bring all the tithes (the tenth) into the storehouse, so that there may be food in My house, and prove Me now by this, says the Lord of hosts, if I will not open the windows of heaven for you and pour you out a blessing, that there shall not be room enough to receive it."