How does Feste's song from Act 2 Scene 3 of Shakespeare's 'Twelfth Night' relate to the themes and characters of the play?

In Act 2 Scene 3 of Twelfth Night Feste enters the scene to have a drink and share some jokes with Sir Toby and Sir Andrew, who are both by this stage very drunk. Sir Toby requests a song from Feste, and this is seconded by Sir Andrew amidst a paragraph's worth of meaningless gibberish that he spews forth in his intoxicated state. Feste asks of the two, "Would you have a love song, or a song …

…mostly directed at Olivia, but as has been said it does carry guidelines for practically anyone in the real world. It seems as though it should have quite a jolly little tune, and if I were to arrange it I would most likely set the underlying rhythm parts for a lute and possibly put a melody for a fiddle as well, these two being classic Elizabethan instruments and both capable of producing light, cheerful tones.