Initially Viola ponders the inkling that Olivia may have mistakenly fallen in love with her:
Viola: I left no ring with her. What means this lady? Fortune forbid my outside have not charmed her.
Viola refers to a moment earlier in Olivia's court (I, v,), where the Duchess ran a critically praising eye from toe to head of Viola's "outside" :
Viola: She made good view of me, indeed so much
That straight methought her eyes had lost her tongue,
Quickly, Viola, resigns herself to the knowledge that Olivia has fallen in love with her:
Viola: She loves me sure, the cunning of her passion
Invites me in this churlish messenger.
The mention of a "churlish" or rude messenger could take a duel meaning. Primarily, the delivery of a ring to symbolize Olivia's affections delivered under the false pretences of it being jeered at. These false pretences are also evidence to "the cunning of her passion" Ironically, Olivia's advance is just as deceitful as Viola's mere presence. Secondly, this may be taken as a blazenly blunt description of the conceited steward, Malvolio.
Viola