The following is from the third chapter of John MacArthur's book, None Other: Discovering the God of the Bible, which is titled, "The God of the Bible is Good and Powerful."
The existence of evil is not an issue that should put Christians on their heels. The answer to why God allows evil in the world is in the Bible. We can know it, we can thoroughly embrace it, and we can enjoy it. Its not an inadequate answer, either. It fully accounts for God's benevolence, His omnipotence, His holiness, and His wisdom. And it exalts His glory. In fact, the answer to the problem of evil begins and ends with God and His glory (pg.50).
Without Sin, God's wrath would never be on display. Without sinners to redeem, God's grace would never be on display. Without evil to punish, God's justice would never be on display. And He has every right to put Himself everlastingly on display in all His glory of all His attributes (pg.63).
God tolerates sin and evil because, in the end, it will bring Him more glory (pg.65).