This is a very complicated question, with many different answers. On the one hand, Isabella is standing up for her own principles when she refuses to have sexual intercourse with Angelo. On the other hand, she is essentially condemning her own brother to death. While Isabella claims that she is acting purely out of religious and moral concerns, she must have some thought for herself as well. She does not want to have sexual relations with Angelo, and she knows that she should not have to do that. Perhaps she is right to protect herself and her principles, especially considering that she believes in an afterlife. But then again, from a more secular perspective she may be seen as being too cold and selfish.
Read more about the dictates around women’s sexuality in Elizabethan England.
Isabella believes that sacrificing her virginity would be a sin, but she claims that she would gladly give her life instead. Of course, this is not really an option, since Angelo has proposed only one solution. Remember that Isabella does not really approve of what Claudio did. She thinks the punishment is just, but she hopes that Angelo might show mercy on Claudio. She sees herself as a virtuous follower of God; otherwise, she would not seek to join a nunnery. It is possible that she views her life as more valuable than her brother’s in the eyes of God because she has not sinned as he has.
The characters in the play could, in most cases, be described according to single words or phrases. Isabella is virtuous and chaste; her brother is cowardly; the Duke is wise; Angelo is a hypocrite. Of these, only Angelo seems to have more complexity to his character, since we see him struggling against the pull of desire. His hypocrisy therefore has more than just one dimension: he wants to uphold his moral purity, but he succumbs to the pull of the flesh.
The play ends in marriage for Angelo and Mariana, Claudio and Juliet, and the Duke and Isabella. Even Lucio will probably be forced to marry a prostitute whom he’s gotten pregnant. This is a traditional ending to comedies, and it provides somewhat of a conclusion, at least suggesting that all the characters are about to embark on another phase in their lives. However, it is not really a happy solution for Angelo or Lucio, who would rather remain bachelors. Isabella’s willingness to marry is unlikely, since she wanted to be a nun. Perhaps the implication is that Isabella joined the nunnery only because she could not find a worthy husband, just as Mariana did not marry because her only candidate left her. This says something about the treatment of women in the play, and their independence or lack of independence.
Claudio is told to resign himself to death, and both the Duke and Isabella offer him words of solace and encouragement. He is still frightened by the prospect and asks his sister to save him at the cost of her virtue. Death is viewed as both a religious passage and the end to the joys of life, and Claudio is most concerned about his ignorance of what it holds. He is not ready to die, though he says he is. Even Barnardine, whom the Provost describes as being unaware of life or death, refuses to be executed. For Isabella, death is a better alternative than sinful sexual intercourse. The implication is possibly that no one is really prepared to die, however they try to convince themselves otherwise.
The Duke offers wisdom and assistance to Isabella, but much of it centers around demonstrating his own power and intellect. He could easily have disclosed his identity early on, freeing Claudio and punishing Angelo, yet he chooses to manipulate the situation through a different persona. He certainly enjoys carrying on his charade, needlessly complicating the decisions to be made and the solutions to the other characters’ problems. Isabella is certainly devoted to the friar, following his every command. It is only natural that she should transfer her affection to the Duke. The occurrences of the play could be described as one long courtship ritual, in which the Duke emerges as a heroic figure by preserving a woman’s chastity, tricking a villain, and saving a man from death.