Every night a part of our neshama goes up to Hashem to get energy for the next day. If one learns very hard during the day or davens with tremendous kavana, sometimes one can dream about what they learned. It may be a dream about Gemara or Chassidus; one’s neshama can even learn NEW things in that dream. One merits such a special dream due to the effort put into davening and learning during the day. ~ Rebbe Yosef Yitzhak Schneerson based on the Zohar.
As an aside, for those of you who are interested, here is a link to a fascinating mind blowing shiur regarding the 9th of Teves (today), Pope Simon Peter and the root of Christianity: http://www.yesodei.org/obm/?p=2255