Parah 5: Third Day Blues
The one who has come into contact with a dead body is impure for seven days. The Cohen sprinkles the mixture of the ashes on the one who wants to be purified on the third and seventh day of his impurity.
We can easily understand why the Cohen must sprinkle the ashes on the seventh and final day of the impurity. It is the end of the process of his impurity. The world was created in seven days, and this person must go through a process of disconnecting from the purely physical in order to be purified from his contact with a physical body that no longer contained a soul. However, why did the Cohen sprinkle the ashes on the third day? Why in the middle of the process? If the idea is to focus on the middle, or center, would it not have made more sense to sprinkle the Ashes Mixture on the fourth day, at the center of the seven day process?
Perhaps the third day relates to the third day of Creation: God commanded the water to gather in pools – Mikvah – and to separate from the dry land. It was a day of separation. It was the day on which water achieved its status as separate from the place of human life, and its status as a purifier. The person who is experiencing the process of seven days of impurity is actually reliving the days of Creation.
It was also on the third day that the earth rebelled against God. The commandment was for the earth to produce trees with bark that was as edible and tasty as the fruit of the tree. The earth, concerned that people would strip away the bark rather than reach for a fruit, produced trees as we know them. The bark is inedible. The earth rebelled. There were seeds of rebellion in the earth from which Adam was formed. Part of the process of purification is to root out our most challenging disadvantage; the difficulty of living with bark as edible as the trees, a life in which our external expressions are perfectly consistent with our internal beliefs. (Machberes Avodas Hashem)