Why did Dimmesdale say, before his death, that God was merciful to him?

He is merciful! He hath proved his mercy, most of all, in my afflictions. By giving me this burning torture to bear upon my breast! By sending yonder dark and terrible old man, to keep the torture always at red-heat! By bringing me hither, to die this death of triumphant ignominy before the people! Had either of these agonies been wanting, I had been lost forever! Praised be his name! His will be done! Farewell.

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