The canons that forbid a woman "in her time" (what a quaint euphemism !) from receiving the mysteries as well as a man who has been defiled by involuntary "nocturnal emission" is related to the teachings concerning the results of the fall.
During a woman's menstrual period, she involuntarily is in a condition which reflects the fallen condition and as a *fallen* creature she should not approach the Holy Mysteries. But like all fallen creatures, she can/should pray.
Men face the same thing with nocturnal emissions etc.
Why is this condition peculiar to women and not men my opinion is that it is because the woman sinned first and therefore bears the greater "mark" of fallenness.
The method in which we give birth is also fallen. Just look at the birth of our Lord for a hint at what might have been: the Theotokos gave birth in a manner that was without pain and that did not violate her physical virginity at any time during the process.
The process of conception, pregnancy and childbirth that we now experience is a direct result of the fall. Therefore, after undergoing this "fallen" process, the woman is similarly not allowed to approach the Holy Mysteries because she has behaved in accordance with her fallen nature. The staying at home and 40 days is simply the way that the Church has been taught by the Holy Spirit to express this truth.
All this talk about "fallen" processes, nature, and behavior is not meant in any way to imply sinfulness or guilt, rather it is the "natural" result of the fall - it is in our nature. This also gives an added dimension to the words of thePsalmist - "I was conceived in iniquity and in sin did my mother bear me". Not that the sexual act is sinful or that guilt is "transmitted" by procreation, but rather that this all takes place according to our *fallen* nature.
Fr David Moser
Edited, from: List: Orthodox Christianity Date: 10 Aug 1994 http://listserv.indiana.edu/cgi-bin/wa?A2=ind9408b&L=orthodox&F=&S=&P=9460