What does the presence of Maria and Sir Toby as characters imply?

"Sir Toby and Maria are two of Twelfth Night’s most explicitly comic characters, since they take themselves less seriously than the play’s romantic leads. (Furthermore, the two noblemen’s very names—“Belch” and “Aguecheek”—seem comically out of place.) These three provide amusement in different ways, however: Sir Toby seems to be an intelligent man and makes witty puns, to which the equally clever Maria is quick to respond. Sir Andrew Aguecheek, however, appears to be a fool. He doesn’t understand Toby and Maria’s wit, as we see when he is forced to ask Maria, “What’s your metaphor?” and “[W]hat’s your jest?” (I.iii.60–64). He is also easily flattered and doesn’t realize certain painful truths—that he is not very witty, that Toby and Maria are making fun of him, and that he does not stand a chance with Olivia."

These two character provide comic relief and because of their positions in the household are allowed to say things that no one else would say. Maria is a perfect example; she's a lady's maid, and yer her comments would never be uttered by a "proper" maid, but she gets away with saying what she likes and is a perfect character for Shakespeare to take license with in the form of dialog.