Is god willing to prevent evil, but not able?
Then he is notomnipotent.
Is he able but not willing?
Then he is malevolent.
Is he both able and willing?
Yes.
Then why cometh evil?
Evil cometh to fulfill the perfect will of God.
For the perfect will of God is manifest in this:
Lucifer sinned (Ezekiel 28:16), and incited autonomy (Genesis 3:5), rebellion, and disobedience in man, and he brought the knowledge of evil to man, for he was a good angel who became evil, and Adam sinned and through Adam, sin entered the world, and death through sin (Romans 5:12), so that the Son of God is manifested to destroy the works of the devil (1 John 3:8) and will be crucified (Matthew 26:39) and will shed His blood (Matthew 26:28).
For God so loved the world (John 3:16) that His Son indeed was foreordained before the foundation of the world, but was manifest in these last times for you (1 Peter 1:20). Know that He was manifested to take away our sins, and in Him there is no sin (1 John 3:5).
Is he neither willing nor able?
Then why call him god?
~Epicurus