The actor who plays Fainall delivers the prologue in which Congreve complains about the high expectations of the audience and the general inability of the poet to please everyone. Congreve also promises that his play will be full of jokes but won’t try to reform the audience.
By starting his play by complaining, Congreve lessens the pressure on himself as playwright. But this is also something of a ruse, as he is perfectly confident of his abilities and does not exactly keep to his word. His play does try to reform the audience but uses humor to point out the vices of society. In having the actor who plays Fainall, rather than Fainall the character (or any other character for that matter, deliver the prologue, Congreve plays with the way that actor’s are in fact only pretending to be the characters they portray and therefore emphasizes, in this play about plotting, scheming, and role-playing, that Congreve himself and the play he has created are the ultimate scheme, the plot behind the plot.