Proverbs 3:9-10
Honor the Lord with your wealth and with the first fruits of all your crops (income); then your barns will be abundantly filled, and your vats will overflow with new wine. 

When we give our tithes to God, we show that we trust and honor Him. Everything we have comes from God, and we are blessed because of our relationship with Him. If we want to live a blessed life, we are to be a blessing. God expects us to tithe into His church on earth so that He can continue to serve the people here.