Everything we have comes from God: Life, happiness, and even our ability to go out and work and accumulate wealth:
"You may say to yourself, 'My power and the strength of my hands have produced this wealth for me.'
But remember the Lord your God, for it is he who gives you the ability to produce wealth,
and so confirms his covenant, which he swore to your ancestors, as it is today."
- Deuteronomy 8:16-17
We give because we are thankful.
We give because we recognize who God is and who we are and
that we are blessed no matter what life throws at us.
We give in order to bless others.