what is Dimmesdale inspired to do at the end of chapter 20?

Chillingworth offers Dimmesdale some of his poison/medicine. Dimmesdale declines the offer and instead orders some food, which he eats "with ravenous appetite." He then sits down and starts writing his sermon, continuing all through the night and even well into the morning.He is writing how election sermon. We get the feeling he is going to finally publicly come clean.