Eastern Orthodox/Mourning period
I am Eastern Orthodox and I'm curious as to why there is mourning on the third,ninth,fourtieth,anniversary and third anniversary? Why these particular lengths of period? Is there a connection with the embalmers of the pharaoh s? We know that they left the body in natron for fourty days?
In the Scriptures, both Old and New Testament, certain numbers have a special meaning.
Three is the number of completeness and perfection.. The Holy Trinity is complete and perfect.
Nine is three threes.
Forty is a number of enormity. It rained forty days and nights in Noah's day. The children of Israel wandered in the wilderness for forty years. Christ fasted for forty days.
Therefore it is appropriate for the Church to guide those who mourn through the process by commemorating the departed on these days.
Customs may vary, but I believe that every anniversary of the death of a loved one is appropriate for a panikhida, and not only the third anniversary.