Why Does God Ordain that there Be Evil?

It is evident from what has been said that it is not because he delights in evil as evil. Rather he "wills that evil come to pass . . . that good may come of it." What good? And how does the existence of evil serve this good end? Here is Jonathan Edwards' stunning answer:

It is a proper and excellent thing for infinite glory to shine forth; and for the same reason, it is proper that the shining forth of God's glory should be complete; that is, that all parts of his glory should shine forth, that every beauty should be proportionably effulgent, that the beholder may have a proper notion of God. It is not proper that one glory should be exceedingly manifested, and another not at all. . . .
Thus it is necessary, that God's awful majesty, his authority and dreadful greatness, justice, and holiness, should be manifested. But this could not be, unless sin and punishment had been decreed; so that the shining forth of God's glory would be very imperfect, both because these parts of divine glory would not shine forth as the others do, and also the glory of his goodness, love, and holiness would be faint without them; nay, they could scarcely shine forth at all.
If it were not right that God should decree and permit and punish sin, there could be no manifestation of God's holiness in hatred of sin, or in showing any preference, in his providence, of godliness before it. There would be no manifestation of God's grace or true goodness, if there was no sin to be pardoned, no misery to be saved from. How much happiness soever he bestowed, his goodness would not be so much prized and admired. . . .
So evil is necessary, in order to the highest happiness of the creature, and the completeness of that communication of God, for which he made the world; because the creature's happiness consists in the knowledge of God, and the sense of his love. And if the knowledge of him be imperfect, the happiness of the creature must be proportionably imperfect.