In Sir Gawain and the Green Knight, what are the three kisses for and what do they mean to Gawain?

In Sir Gawain and the Green Knight,
Gawain travels to meet the Green Knight so that the other may take his turn at beheading
Gawain, as they had agreed a year prior. Gawain arrives at his destination early.
Finding a castle nearby, he requests the lord's hospitality, which is eagerly
granted.

The lord is Bertilak (secretly the Green Knight, a
shape-shifter). He welcomes Gawain, and suggests that while he passes the Christmas
holiday with the lord and his wife (Lady Bertilak), that they share the fruits of their
labors each day. So when Bertilak goes out hunting the first day, he returns with his
kill which he presents to Gawain. In the meantime, Lady Bertilak has been attempting to
seduce the noble Gawain, but he resists, exchanging only a kiss. When Bertilak returns,
Gawain presents the kiss he has received that day from the lady, to his host. The next
day it is two kisses, and a different animal. The third day, three kisses, and a
fox.

In all of these situations, Gawain is honest with
Bertilak (except for the magic sash which is supposed to save him from death—he hides
this). In the life at court, a kiss was not a betrayal, and Gawain returns the
kiss/kisses to Bertilak each day.

If we are looking for
symbolism for the three kisses, we might look to the three temptations of Christ by the
Devil. First he tempts Christ to prove himself by turning stones to bread. Jesus
refuses. Satan's second temptation is that Christ throw himself down from the top of the
temple, for surely God's angels will save him, but Jesus refuses. The last temptation is
an offer: Satan takes Christ to the top of a mountain and promises that Christ will be
lord of all he sees if he will bow down and worship Satan. A third time, Jesus
refuses.

Literally, Lady Bertilak tempts Gawain three
times. Figuratively, this may be an allusion to the three temptations of Christ—remember
that Gawain, as a true knight, serves not only Arthur, but more importantly has taken an
oath to the Church; his patroness is the Virgin Mary. All he does is in service to her,
and she inspires him.

Gawain is tempted three times with
three kisses; he does not keep them for himself, but returns them to Lord Bertilak.
Bertilak later admits that he used his wife to help test Gawain to
see if he was as noble, honorable and trustworthy as Arthur's knights, especially
Gawain, were reputed to be.

Whether as simply a literary
figure, or as a symbolic character compared to Christ, Gawain withstands
temptation.