It’s a good time of year to ask that question, because the traditional Christian celebration of Pentecost gives us an answer.
Jesus told his disciples in Luke 24:49, “I am going to send you what my Father has promised; but stay in the city until you have been clothed with power from on high.” So the disciples are going to receive “power” – but power to do what, exactly?
They’re about to find out, because only a few weeks later on “the day of Pentecost” in Acts 2:1 “they were all together in one place” when “Suddenly,” verse 2, “a sound like the blowing of a violent wind filled the whole house where they were sitting,” and “All of them were filled with the Holy Spirit,” verse 4. And in verse 38, this same Holy Spirit was also promised to anyone who acknowledged that through Jesus all their sins had been forgiven: “You (too) will receive the gift of the Holy Spirit,” Peter said.
So, first of all, we have Jesus’ disciples being “clothed with power from on high” as promised, and now the same promise being opened up to “you and your children and for all who are far off,” verse 39. It’s obviously important, then, that the power of the Holy Spirit be given to people, but what for?
That’s answered by Peter in verse 40, when he “pleaded” with his listeners, “Save yourselves from this corrupt generation.” Or as another translation phrases it, Peter “urged them over and over, ‘Get out while you can; get out of this sick and stupid culture.’” Peter repeated that later too, in 2 Peter 1:4, when he wrote that God “has given us his very great and precious promises, so that through them you may participate in the divine nature and escape the corruption in the world caused by evil desires.”
In answer to the question, then, as to why God, who has the power to stop evil, doesn’t stop it, Peter offers us an answer: God IS stopping evil, by giving US the power to stop it. And what better solution to evil is there, than that? God could, of course, just blast evil people into oblivion, or sizzle to a crisp anyone thinking an evil thought, but if he did that how many of us would be left? Not me, for a start, because I know what unsavoury thoughts I have toward neighbours whose dogs never stop barking, or toward politicians who lie through their teeth.
And doesn’t that illustrate the source of evil? It’s what’s going on inside our own heads, just as Jesus said in Mark 7:23, that “All evils come from inside” us. Conquer what’s inside us on a worldwide scale, then, and evil would be eradicated, which is exactly what God had in mind on Pentecost, to give us the chance at last to eradicate evil right at its source, inside ourselves.
The problem with that is the massive influence of the sick and stupid culture we’re stuck in. But “You, dear children,” John writes in 1 John 4:4, “are from God and have overcome them, because the one who is in you is greater than the one who is in the world.”
We have the power IN us, then, to “not conform any longer to the pattern of this world,” Romans 12:2, and instead “be transformed by the renewing of your mind.” I can have a mind that can see through the sick and stupid thinking of the culture, and therefore not be taken in or influenced by it.
So in answer to the question in the title, God IS using his power to stop evil, through his promise of the Holy Spirit filling people with his nature instead.