We've just witnessed Angelo's conflict of interests: he wants to (strictly) enforce his law on lechery while desiring to have relations with Isabella. Shakespeare represents him as a contradiction. However, Duke Vincentio comforts Isabella by saying that Angelo is testing her virtue and was pleased by it. It is interesting to see how Shakespeare demonstrates a belief that there are certain acts/sins worse than others, and possibly deserve reasonable punishment. For example, Duke's conversation with Juliet compares her pre-marital actions with Claudio's, debating which is more punishable. One of Shakespeare's themes is this moral dilemma of determining sinfulness of sin, while saying that death isn't as bad as it seems.
