The Midrash “BeShalach”: The sea will retreat to the sides when it sees the children of Israel before it, carrying the coffin of Joseph. Just as he fled from the wife of Potiphar, so will the sea retreat for his descendents.
Question: Why does the sea have to retreat to the sides?
Answer: Since Joseph unites everyone. Joseph is Yesod, the point where all of a person’s attributes connect for the sake of the Creator. It is actually Yesod that creates an inclusive chunk of attributes that are totally opposite.
“To carry Joseph before the children of Israel” means to advance in complete unity among them. The sea symbolizes Din, the force that is opposite from unity, that is opposite from life. If you walk on it with the point of unity, like with a battering ram, the sea will retreat to the sides.
From KabTV’s “Secrets of the Eternal Book” 4/30/14