Giving is an important part of a worshiping follower of Christ. By giving we acknowledge that all we have is a gift from God. It therefore proclaims Him. Returning part of His blessing acknowledges God as a giver, follows His command to give, and when done with a cheerful heart, it offers thanksgiving to Him.
"Each of you should give what you have decided in your heart to give, not reluctantly or under compulsion, for God loves a cheerful giver."
-2 Corinthians 9:7