I've listened to several people recently talking about the contrast between depictions of God in Hebrew Scripture and the New Testament. Of course, it's not clear cut – but I can see why people like the 'God of the New Testament', (as if there were two), better.
So, this poem is partly about that (false?) contrast; but also about the implications of forgiveness. How do we feel about a repentant Myra Hindley? Or a repentant Hitler? A repentant Serpent? A repentant Judas? Do we tolerate the idea of forgiveness?