When you try to create water, you figure out you cannot because energy cannot be created or destroyed. Also because only He can create water.
When you go to chop a piece of wood, you can chop it into as many pieces as you like, but it is not destroyed. So then you throw the wood into a fire. The wood becomes ash but is still not destroyed. You cannot do anything else to change the wood. This teaches us not only that energy cannot be destroyed, but also that energy keeps changing forms.
