In The Way of the World, is Mirabell worthy of uttering the moral of the play as stated in the last four lines of the play?
He states "From hence let those be warned, who mean to wed; Lest mutual falsehood stain the bridal bed; For each deceiver to his cost may find, That marriage frauds too oft are paid by kind."
This is a great question to think about, because opinion of Mirabell is often sharply divided. On the one hand, he is an immensely attractive character that the audience can't but help but like, as he is intelligent, young, handsome and rather headstrong individual who is clearly suffering because of his unrequited love for Millamant. He is definitely a charming figure, and the way in which he shows how much he is in love endear him to us as an audience.
However, at the same time, it is clear that he is motivated by cynical self-interest, and he is something of a character in terms of his former relations. He had a relationship with Mrs. Fainall and deliberately deceived Lady Wishfort in the past by pretending to be in love with her. He is a manipulative individual, who uses his charm and skills to marry Millamant and get his hands on her dowry. The play gives ample evidence of how he exploits both his friends and servants to get what he wants.
Therefore Congreve's choice of giving him the moral of the play in the final lines is a rather interesting one. Mirabell on the one hand, because of his treachery, deceit and previous relationships, can hardly be used as a moral mouthpiece. However, on the other hand, the way in which he marries Millamant for love and also exposes the adultery of Fainall and Marwood perhaps would suggest that he is the character who acts as a champion of true love and therefore is the fitting choice.