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:

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"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:

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"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.