Mehregan is the most important ancient Iranian festival, after Norooz. As in all other festivals we have inherited from our ancestors, Jashn-e-Mehregan too is celebrated with singing and dancing and praying. In all of our festivals offering food to everyone was and still is part of the celebration.
In older days this was specially important as was a way for families who were better off to give away food to those less fortunate than them, in a way that it did not hurt their dignity.
The offering customarily were Bread, Cooked Dried Meat and Lork which was a mixture of dried nuts and fruit, all of which could have been kept for days. For some families these would have been more nutritious food than they could afford to provide for themselves.
Dear Atria, the Iranian culture is very rich and is based on so many rich foundation which have been developed in nearly 3000 years. I don't claim to understand it all, nor I claim to know the reasoning behind them all. In fact, I am of the view that making such claims shows the inadequacy of the knowledge of claimant on the subject.
The Mehregan festival believed to have been the Harvest festival, but as all other Zoroastrian and Iranian festivals was and is about friendship, peace, harmony and love.
Mehregan also believed by some to commemorates other things, including the triumph of good over evil and warmth over coldness, the victory of light over darkness, achievement of knowledge as oppose to ignorance and other things signifying that good always has and always will triumph over bad and evil.
Different stories are told about Mehregan Festival, its origins and the time it was celebrated. As with everything else that was originated several centuries ago, each story is as likely as the other and because the origin dates back several many hundreds of years there is no sure way to validate any of them.
However, I read about evidence having been unearthed showing that over 11,000 years ago there was agriculture sites in Iran. The archaeologists have even discovered at a site in Zagros Mountains Ancient Mortars and Grinding Tools showing that 11,000 years ago people in Iran were grinding Wheat and Barley or whatever else they may have been harvesting at that time.
For the above reason I believe Mehregan to have been a harvest festival which at later stage have been improved by becoming associated with Zoroastrian religion.
Let me know if you believe otherwise, and why.