According to
Claudio,
Angelo is likely handing down a steep and rarely-used punishment in this case so that he can demonstrate his unyielding authority and set an example to others who might have sex out of wedlock.
Lucio agrees and recommends that Claudio seek the
Duke's reprieve. However, Claudio responds that he has tried, but the Duke is nowhere to be found. Claudio then asks Lucio to alert Claudio’s sister,
Isabella, in the hopes she may help him. Isabella has just joined a nunnery, and Claudio is optimistic that she may be able to persuade the authorities to free him. Lucio vows to find Isabella swiftly.