Generous giving is a response to God's great love and His generosity towards us. It is an act of gratitude, faith, and obedience- it's a reflection of the heart.
When we give, God honors our act of faith and obedience. In Malachi 3:10, God asks the people to test Him by bringing their tithes to the temple. He promises that if they do, He will open the "windows of heaven" and pour out a blessing so great that they will not have room enough to receive it.