The human body is a fragile thing. Just a fall, a few days without water, exposure to temperatures too cold or too hot; and our bodies will cease to function. It is not our physical frame, a shell of flesh and bone, wherein we find our real strength, but from the inexplicable spark within that drives us to go on when there seems to be nowhere to go. It is an ineffable quality that fortifies our emotions and steels our mental toughness beyond mere corporeal matter.
For Christians, we know that it is God living in us that generates that power which holds us together when our frail vessels should fall apart. While it is unlikely that one would put a treasure in brittle clay container, God came to live inside the vulnerable human heart to make us stronger than we could ever be without Him.