When 2 Peter’s apocalyptic schema is understood rightly, as the destruction of all that separates creation from God, that purifies and radically transfigures the broken creation, his fixation on the transfiguration of Jesus becomes more clear. The transfiguration is a sort of pre-appearance (my term, not Harink’s) of the final divine apocalypse that transfigures creation and dissolves all that is opposed to communion with God.
This is seen further in the contrast between the disciples’ response to the transfiguration and that of Moses and Elijah. The disciples are shocked senseless and barely know how to talk coherently (“he did not know what he was saying”). Moses and Elijah, however stand calmly and talk to Jesus about his mission in Jerusalem. They stand as those already taken up into God’s apocalypse, abiding, conversing, and indeed, relaxing within the glory of the Lord. The disciples however are not ready for this. They have to go through the fire of the transfiguration — which leads to and through the cross — to be prepared to rest in this radical, transforming glory.