"Will a mere mortal rob God? Yet you rob me, but you ask how are we robbing you? In tithes and offerings." Malachi 3:8
Malachi asks a hilarious question. It is crazy to think you can get away with robbing God; He is the All-seeing Almighty Lord of the Universe. God as Ruler and Creator already owns all things, what we have is ultimately His and we are managers. He is not fooled that we haven't given back an acknowledgement of His favor.
We do not give to God to buy his favor, because he has already given it. God has been generous to us, and he is capable of lavish blessings. It is morally right to give back to him because it is an acknowledgement of his generosity.
Jesus said "Render to Cesar what belongs to Cesar and render to God what belongs to God." (Matthew 22:20-22). God has a right to expect us to give tithes and offerings. He has given commands in his Word to bring offerings including thank offerings, first fruit, vows, giving for the poor, sharing with those who minister His Word and good old fashioned tithes.
WHAT IT SAYS
He has been generous to us and he is watching to see if we will be as generous. It is our sacrificial giving that proves we are the sons and daughters of the One who "so loved the world that he gave his only begotten son..." (John 3:16). If this is the nature of the Father it should be the nature of the children.
The Lord has a right to ask us to give. No one likes to be robbed and it is dangerous to rob the one who is All Powerful. In patience He has not dealt with us in judgment- but it is not wise to try His patience.
Resolve today to give back to God, be it through your faith community or a worthy charity that honors Him, and do it today. Don't do it because you hope to buy his favor, (you already have that; he gave his son for your sins), but because it is the right thing to do.