In his sermon on Romans 4:16–21 (9/26/1999), John Piper directly addresses the children and illustrates how faith glorifies God. Listen from 27:28 to 33:30.

Here’s what’s in the sermon manuscript (which isn’t a transcript):

Let’s illustrate this for the children. Your daddy is standing in a swimming pool out a little bit from the edge. You are, let’s say, three years old and standing on the edge of the pool. Daddy holds out his arms to you and says, “Jump, I’ll catch you. I promise.” Now, how do you make your daddy look good at that moment? Answer: trust him and jump. Have faith in him and jump. That makes him look strong and wise and loving. But if you won’t jump, if you shake your head and run away from the edge, you make your daddy look bad. It looks like you are saying, “he can’t catch me” [i.e., he’s incompetent] or “he won’t catch me” [i.e., he’s mean] or “it’s not a good idea to do what he tells me to do” [i.e., he’s unwise]. And all three of those make your dad look bad.

But you don’t want to make God look bad. So you trust him. Then you make him look good—which he really is. And that is what we mean when we say, “Faith glorifies God” or “Faith gives God glory.” It makes him look as good as he really is. So trusting God is really important.

And the harder it seems for him to fulfill his promise, the better he looks when you trust him. Suppose that you are at the deep end of a pool by the diving board. You are four years old and can’t swim, and your daddy is at the other end of the pool. Suddenly a big, mean dog crawls under the fence and shows his teeth and growls at you and starts coming toward you to bite you. You crawl up on the diving board and walk toward the end to get away from him. The dog puts his front paws up on the diving board. Just then, your daddy sees what’s happening and calls out, “Johnny, jump in the water. I’ll get you.”

Now, you have never jumped from one meter high and you can’t swim and your daddy is not underneath you and this water is way over your head. How do you make your daddy look good in that moment? You jump. And almost as soon as you hit the water, you feel his hands under your arms and he treads water holding you safely while someone chases the dog away. Then he takes you to the side of the pool.

We give glory to God when we trust him to do what he has promised to do—especially when all human possibilities are exhausted. Faith glorifies God. That is why God planned for faith to be the way we are justified.

(This is from sermon 52 of 225 in Piper’s 155-hour series on Romans. I recently began listening straight through it. Rich.)