Cyrano de Bergerac is written in a morally elevated tone. It's clear that the play's creator, Edmond Rostand, had a very firm set of moral values that he wished to promote through the actions of his most important character, Cyrano himself. The eponymous hero is presented to us as a man of exemplary virtue and integrity, a man of high moral values who's prepared to keep his word, even at great cost to himself.
Cyrano maintains his integrity until the bitter end, refusing to reveal himself as the author of Christian's letters to Roxane. Some have interpreted his behavior as almost masochistic, but another way of looking at it is to say that Cyrano's deadly serious about keeping his promises, an attitude that was all too rare, then and now.
To some extent, Cyrano is the living embodiment of an ancient code of chivalry that was dying out in the seventeenth century, when the play is set. His absolute integrity and devotion to duty act as a reminder of how society has declined morally. We may not agree with everything that Cyrano does, but we can still respect and appreciate his unswerving fidelity to what he believes to be right. In that sense, he stands as an example to us all.