Political Science professor Fred Baumann writes in The Weekly Standard:
Holding together with apparently effortless ease the most intensely characterized opposites is, to me, the essential quality of Mozart's music and the state of mind it engenders. Another operatic example is the famous quintet in the first act of Cosi Fan Tutte where, to the most soaring and blissful music, two couples of lovers mourn the departure of the men for war, while an elderly cynic (who, for a bet with the two men, is merely setting up a test of the women's fidelity) mutters that he'll die if he can't start laughing.
This is not mere ironic deflation of romantic pretensions. Just as we know the protestations of eternal love to be foolish, we feel their present truth and feel pity for the vulnerability they reveal. There is a similar moment at the end of Le Nozze di Figaro, where the countess pardons the count, in which much-betrayed, but still-loving, mercy balances perfectly with resignation and bitter necessity.
We get it. We feel all of it. No comment is needed.