"What name to call thee by, O virgin fair, I know not, for thy looks are not of earth And more than mortal seems thy countenances"

The quote by Petrarch radiates the quintessential reverence and love that is characteristic of Petrarchan sonnets. In this line, the speaker is revealing his wonder for the subject's charm and essence, which goes beyond earthly attributes. The expression "What name to call thee by" symbolizes the speaker's sense of insufficiency in discovering a fitting homage for her. This shows a typical style in Renaissance poetry where the beloved is typically portrayed as possessing an otherworldly, divine quality.

The term "O virgin reasonable" acts as an epithet that not only highlights her appeal but likewise connotes purity, suggesting an untouched, idealized perfection. This lines up with the middle ages and Renaissance perfects where physical charm was often related with ethical and spiritual virtue. By describing her as a "virgin", the speaker is elevating her to an almost saint-like status, highlighting an untouchable and heavenly quality that is beyond reproach.

"I understand not, for thy looks are not of earth" further highlights her celestial nature. The speaker acknowledges his confoundment, suggesting that her charm is so profound and remarkable that it can not be recorded by human language or confined to earthly descriptors. It suggests a Platonic suitable, where her physical look is just a reflection of a greater, more best realm.

The line "And more than mortal seems thy countenances" deepens the supernatural impression by suggesting that her whole being appears to be more divine than human. In this expression, "countenances" mentions her expressions or existence, which are represented as surpassing simple mortals. Petrarch is utilizing embellishment to communicate a level of affection that verges on worship, a common device in which the cherished is idealized to the point of being unattainable and best.

In essence, this quote catches the ineffable nature of idealized love and beauty, a main theme in Petrarch's works, showing the stress in between earthly love and spiritual or magnificent love.