Have you ever played with that modeling clay that got left out of the container? It turns hard like a rock! If we try to make a figure with it, it cracks and breaks. The Bible says that when we're stubborn (when dad says "don't do that" and we do it on purpose anyway), our heart becomes just like that hard clay.
But when we revere God (when we listen with respect and obey right away), our heart stays nice and soft, just like brand-new clay! Then our Father in Heaven and our parents can shape us into strong, smart, happy kids.