“You gotta have faith,” people say. But what does that mean? Is any faith good faith?

“Believe in yourself and all that you are,” wrote one positive thinker a century ago. “Know that there is something inside you that is greater than any obstacle.” As nice as that platitude may sound, it falls to pieces when it crashes into reality. We need a faith in something bigger than ourselves. 

God promised Abram he would have a multitude of descendants (Gen. 15:4–5), so he faced a huge obstacle—he was old and childless. When he and Sarah got tired of waiting for God to make…