The speech of the Duc de Grammont, who has grown "magnificently old," demonstrates that the nobleman now recognizes truer values than he has in his younger years when he desired Roxanne and planned to use the Vicomte de Valvert as a suitor to Roxanne so that he could be close to her. For, in this monologue the Duc expresses his envy for Cyrano de Bergerac, who has never been a hypocrite.
...There's such a thing as success
Which sickens like excess. When a man wins
The big prizes--having no glaring sins
To reproach himself with, filling the foreground up--
He feels sinful nevertheless, defiled from top
Reflecting upon his own life, the Duc feels a certain contamination--"a vague disquieting breed of vermin"--for having compromised noble values in the interest of his political advancement and satiation of his lust for Roxane. Now, he says,
The ducal robe sweeps up the endless stair
With a dry rustle of dead illusions, a sere
Whistle of regrets.
For de Bergerac, however, there are no regrets; he has lived his life freely, answering to no man, instead satirizing the politicos and the flatterers. Throughout the play, Cyrano is uncompromising in his morals and values. In fact, he represents the type of man that the Duc wishes he could have been. Therefore, the significance of the Duc's speech in which he praises untarnished virtue such as Cyrano possesses is that this speech is an underscoring of a theme of Rostand's famous play, that of values and virtues.