Suffering is to purify, not for punishment

Mitteler Rebbe, Toras Chayim, Bereishis Miketz 219c

It is not possible that all the suffering stems from Israel being suited for punishment, because the sins do not rise to the degree of the hard and bitter suffering that truly reaches the very depths of the soul. And even for the little bit of good that is done, it is fitting to sit in peace, as we find by Nevuchadnezzar that because he took three steps in honor of Hashem, greatness was decreed that he and his sons for three generations -- and there is no Jew who hasn't honored Hashem much more than this!

We are forced to recognize that the main purpose of the suffering that comes upon a person is "לבטל את גסות רוחו" to nullify his coarseness and ego and only to make him humble and submissive [and not as a punishment for sins].