In Chapter 4 of his book, Prayer, Tim Keller writes:

Speech-act theory makes a convincing case that our words not only convey information; they get things done. However, God's words have power infinitely beyond our own. God's words are identical with his actions … We humans say, "Let there be light in this room," but first we have to make sure the room has been properly wired. Then we have to walk across the room and flick a switch, or go to the cabinet and grab some matches so we can light a candle. Our words need deeds to back them up and can fail to achieve their purposes. God's words, however, cannot fail their purposes because, for God, speaking and acting are the same things.

Possible Preaching Angles: This illustration could also be used as an object lesson by walking over and turning on a light switch or holding a candle and using a lighter to light it.