The rules of Persian law did not allow the king to simply cancel his order to allow the enemies of the Jews to attack them. So instead, he sent a new decree allowing the Jews to arm, gather and defend themselves. Notice that in at least two ways this was even better than cancelling out the original decree: first, the Jews were able to defeat many of their enemies permanently. Second, many people actually became Jews. The evil law was used to bring about greater evangelism to the true God!
At times in our lives, we face difficult situations that we would prefer for God to simply erase. Often, however, God chooses instead to turn those difficult situations into an even greater opportunity to demonstrate his power. If God has not responded to your request to change the situation, don’t give up hope: perhaps His plan is to use even what seems to be evil, to bring about a greater good and to spread the gospel of Jesus Christ to the world.