Evil was necessary because without it free will was impossible, and without free will there could be no growth—no forward movement, no chance for us to become what God longed for us to be. Horrible and all-powerful as evil sometimes seemed to be in a world like ours, in the larger picture love was overwhelmingly dominant, and it would ultimately be triumphant.
Eben Alexander (2012). “Proof of Heaven: A Neurosurgeon's Journey into the Afterlife”, p.48, Simon and Schuster