During their travels in the wilderness, the Israelites complain about the lack of water and food.  When the Israelites reach Marah, known for its bitter waters, God instructs Moses to throw a piece of wood into the water, and the water becomes sweet and suitable for drinking.  Shortly after this, God addresses the peoples’ complaints regarding their lack of food, by providing the Israelites with quail in the evening and manna in the morning.  On Friday, the Israelites are instructed to gather a double portion of manna, the first one for Friday and the second for Shabbat.  

“And the children of Israel came to Marah.  And they were not able to drink the water at Marah for they were bitter” (Ex. 15:23).  The Kotzker Rebbe explained the words “for they were bitter” as referring to the people themselves, not the water.  When someone is bitter himself, everything tastes bitter.  This concept holds true in many areas on life.  If a person feels bitter, nothing in life appears positive.  Anyone looking for faults and defects will always be able to find them.  A bitter person makes himself miserable and those in his environment suffer with him. While he thinks that he has valid reasons for considering things to be bitter, the source of the problem is not out there but within himself.  By sweetening one’s own outlook one will live in a much sweeter world.