"The Virgin Mary is not the great exception, she is the great example."

Orthodox Christians celebrate the Feast of the Meeting (or Presentation) of the Lord in the Temple on February 2.  The Western church celebrates the Purification of Mary on the same day; this feast is also referred to in the West as Candlemas as this was the day candles were blessed. 

While the East centers its liturgical focus on Christ meeting Simeon and Anna (and being seen by Simeon as the Messiah incarnate), the West centers its liturgical focus on Mary fulfilling the law by being purified from her childbirth after 40 days.  That said, neither focus is held to be inherently more important than the other in either East or West. For Eastern Christians, though, the term 'purification' implies at least the possibility that the Virgin Mary did something wrong - something that required purification.

We know of no sin committed by the Virgin Mary (though St. John Chrysostom mentions in his homilies that the Virgin was guilty of pride - especially at the Wedding at Cana, years after the event commemorated by this Great Feast, of course). But, we should not forget, as Fr. Alexander Schmemann is known to have said: the Virgin Mary is not the great exception, she is the great example. If Christ is the icon of salvation, the Theotokos is the icon of the saved. 

If this is true, from what then does the Theotokos come to be purified? Fr. Thomas Hopko explains:
...the scriptures teach that all human beings who are inevitably caught up in the falleness of the sinful world, are in need of "purification" when they come into direct contact with God, and especially when they are objects of direct divine action. God is always acting in our lives...These are also the times of worship, such as when the priests go into the Holy Place or when they touch the Holy Objects. thus, according to the Mosaic law, mere human beings who were in direct tough with God through His concrete divine actions were required to offer signs of ritual 'purification' to express the fact that being mere mortals and victims of sin not to say sinners in their own right in virtually all cases) they had also the objects of the holy actions of the Most High and Holy God. (The Winter Pascha, p. 176)

Lest we forget at any time, the Virgin Mary inherited the same mortal corruption as the rest of mankind. She still had to obey the law, she still had to die, and she was in need of our Lord's crucifixion and death along with the rest of us. The Feast of the Meeting / Presentation / Purification reminds us Mary was in this way 'simply human' even though she had the most direct, immediate communion with God Himself - and while the priests of Israel (and we ourselves) can only commune with God in a mystical, less direct way than the Birthgiver and Mother of God. 

This is why the Theotokos, Mary, is deserving of all honor and all praise. And this motherhood of/to the Divine is why she is so a powerful an advocate for us with her Son: God.