I put the question to my parents and to my blog readership, and all who responded--2 parents and 2 readers--disagreed with the sign. As my father-in-law put it, that's "a little presumptuous."
This sign message needs to be qualified in some ways, because I think there are in fact some times faith knows he will. I know that he will complete my salvation/sanctification (Php 1:6). I know that Jesus Christ will come back. I know that the Church will not ever be wiped from the face of the earth by her enemies.
But there are a lot of areas where faith is simply knowing God can. I pray my neighbor will be healed of cancer and live a long life here on earth as wife and mother. I know God can do it, but I don't know whether he will.
I readily admit some people have what that church sign asserts, a faith that knows God will.
- David knew that he would slay Goliath: "This day the LORD will hand you over to me, and I'll strike you down and cut off your head. Today I will give the carcasses of the Philistine army to the birds of the air and the beasts of the earth, and the whole world will know that there is a God in Israel" (1 Sam 17:46 NIV).
- Elijah knew that God would light his sacrifice up with heavenly fire: "Then you call on the name of your god, and I will call on the name of the LORD. The god who answers by fire—he is God" (1 Kings 18:24 NIV).
I think what David and Elijah had was a unique, Spirit-given insight into what God would do. It might be the spiritual gift of faith that some have and many do not (cf. 1 Cor 12:9).
George Muller appeared to have this kind of faith. I remember an account of him sailing, and he was told of bad weather, and he prayed that the weather would clear up, and he knew that it would do so, telling the sailors to proceed forward and not turn back. And the weather did clear up.
That's my neat little theology. But where God's Word shakes up my theology is with verses like Mark 11:22-24: "Have faith in God," Jesus answered. "I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours" (NIV).
Some people have helped shed some light on that for me, but I still need more light.