To what does Romeo compare Juliet when he meets her for the first time in Romeo and Juliet?
When Romeo and Juliet actually meet one another for the first time he addresses her as follows:
"If I profane with my unworthiest hand
This holy shrine ... "
Romeo is comparing Juliet to a sacred being. Her residence is therefore a shrine to her. The suggestion is that she is some kind of saint, a being far beyond the reaches of ordinary humans. He therefore humbly beseeches her to allow him penitence for having "profaned" (i.e. desecrated) this place consecrated to her.
" ... the gentle fine is this:
My lips, two blushing pilgrims, ready stand
To smooth that rough touch with a tender kiss."
The punishment for his disrespect would be "a gentle fine" in which he would smooth away the roughness of his unworthy touch. This fine should be in the form of a tender kiss.
The metaphor of a shrine for the saint, Juliet, is extended when Romeo names his lips "two blushing pilgrims". The implication is that his lips are embarrassed and shy and as "pilgrims", he suggests that they have made a long journey to show their allegiance and veneration for their saint (Juliet).
Pilgrims often undertake long and arduous journeys to a holy place as a symbol of their humility and to show their allegiance to, and respect for, a saint or heroic character.
In these few words, Romeo displays his deep attraction, respect and affection for Juliet. She is beyond ordinary and should be served and treated like a sacred entity.
It is clear that Juliet understands the allusion when she says:
"Good pilgrim, you do wrong your hand too much,
Which mannerly devotion shows in this;
For saints have hands that pilgrims' hands do touch,
And palm to palm is holy palmers' kiss."
Romeo's comparison of her to a saint quaintly encourages her to call him a "pilgrim" which is an apt title within the context of their tete-a-tete.
When Romeo and Juliet first meet at the party at the Capulet's mansion, Romeo is clearly overwhelmed by his first sight of Juliet, and when he has asked a servingman the identity of this mystery woman, and received no answer, he goes on to describe her in the most glowing of terms, comparing her a precious jewel being used for an earring:
It seems she hangs upon the cheek of night
As a rich jewel in an Ethiop's ear--
Beauty too rich for use, for earth too dear!
Romeo thus compares her to a "rich jewel" hanging in an "Ethiop's ear," suggesting that she almost represents a star hanging in the night sky, because of her beauty. Note the way in which the value of this "jewel" is highlighted as being "too rich for use" but also so beautiful and precious that it is "too dear" for earth. Romeo therefore describes Juliet in the most glowing of terms when he first lays eyes upon her.