When we give, we worship.

Worship also means to honor, and so we honor God with giving back to him a portion of His provision. You cannot give more than God, and giving back to Him adds to your subtraction.

God gives us one opportunity to test him, and that is through our obedience in giving (Malachi 3). 

Giving brings with it a promise of provision (Proverbs 3:9,10).