A caterpillar changes...
Its not just a change he can put right.
We have a chance every time we change.
We have the choice of repentance.
A caterpillar changes into a butterfly.
It gets on with it and has no going back.
Whatever he did as a caterpillar doesn't matter anymore.
If he repents All shall be forgiven and forgotten.
If he doesn't repent God is the most merciful, but the most severe in punishment.
A human evens out to the same situation.
We are compared to caterpillars as this is truth of our life.