Think about it for a moment. Every surgical site on the human body "naturally" grows together and closes up. Even non-surgical openings that are no longer needed, like the 'ductus arteriosus' in an infant's heart, grows closed after birth - as it is no longer needed to balance the pressure between the chambers of the baby's heart.
Yet, the Almighty ordained that our navels (aka "Belly Buttons") remain intact in the center of our bodies. Why did Hashem design us in such a way that this remnant of our in-utero total state of dependency remain with us throughout our lifetime?
The Torah tells us that the Meraglim (spies) died a death befitting ("measure for measure") their transgressions. They asphyxiated, worms exited their tongues and re-entered their bodies through their navel! What possible significance of "measure for measure" could worms entering their navel be? And of course... why do all human beings have navels anyway?