Epecurious

Is God willing to prevent evil, but not able, then he is not omnipotent

It is man who must end evil and can be done only through Christ. Since so few believe, ergo evil.   

Is he able but not willing? Then he is manevolent. 

Only man causes evil.  Since all good comes through God, a storm that kills many is not an evil thing, you may not like it but to eternity it is of no consequence. Your eternal soul on the other hand has consequense.

Is he both able and willing then whence commenth evil ? 

The only freewill man has is to accept or not accept God. Evil comes from those that fail to love Christ and to love Christ is to love the least of us. How can there be evil if you love your enemy and the poor over all ?  

Is he either able nor willing  then why call him God 

He is able and willing.