"for where your treasure is, there your heart will be also."
Much like giving our time in ministry, giving of our financial resources is another way that we obey God and express our dependence upon Him. The biblical precedent is that your firstfruits would go towards “General Tithes and Offerings” with anything above that being used for supporting ministries above your normal tithes.
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.