What is faith?

"Faith is not that human notion and dream that some hold for faith . . . when they hear the gospel they fall-to and make for themselves, by their own powers, an idea in their hearts which says, 'I believe.' This they hold for true faith. But it is a human imagination and idea that never reaches the depths of the heart . . . Faith, however, is a divine work in us . . . Oh, it is a living, busy, mighty thing, this faith . . . Faith is a living, daring confidence on God's grace, so sure and certain that a man would stake his life on it a thousand times. This confidence in God's grace and knowledge of it makes men glad and bold and happy . . . Beware, therefore, of your own false notions and of the idle talkers, who would be wise enough to make decisions about faith . . . Pray God to work faith in you; else you will remain forever without faith, whatever you think or do." - Martin Luther