Divine Law of Supply and Demand

What my God should supply all your needs according to his riches and glory. Phillipians 4 19.  We have to supply all our needs, but if it doesn't work without us believing, how is it that we should express our faith in the area of finance? It takes faith to give away a portion of what we have and trust that we have enough. If there were no God, and if his promise of multiplying I would give back to us was not true, it would be stupid to give. But there is a God who is true, to his promise. When we give we express that faith. People who are not giving because they do not have enough are people who don't believe. But phillipians has proof that faith through that giving. Some people have used the word Need to say they are only the bare neccessities. And the word supply came from the greek word PLEROO which means to Replenish.