We prove ourselves to our creditors by paying our bills according to our agreements with them. We prove ourselves as responsible citizens by obeying laws. And for any of those things we don't do that we should, it's proof, too. When we have irrefutible, indisputable evidence of proof, then we can stand firm in that which we know because it has been proven to us. When something has been proven to you, doubt is banished.
Fear is gone.
By being tested. Yet, that is how God proves Himself to us. Instead of us standing on the proof of our deliverance through salvation, instead of us standing on the abundant mercies He has extended to each and every one of us, instead of us remembering all the blessings He has already sent our way, we cave in. Note emphasis on the word should . We don't fall back on the promises of God, the many marvelous things He has done for us already.