Q. Who thought of Tashlich?A. Possibly the prophet Isaiah, who in chapter 1 of his book speaks of sins that are as red as scarlet becoming as white as snow (verse 18) and says that it will not happen magically without our own effort: “Wash yourselves, make yourselves clean” (verse 16).
The term Tashlich (“You will cast”) derives from Micah: v’tashlich bim’tzulot yam kol chatotam, “You will cast all their sins into the depths of the sea” (7:19). Since water cleanses the body, it is the symbol of cleansing the soul.
The Midrash says that Satan (the personification of the forces of evil) turned himself into a river in order to stop Abraham and Isaac reaching Mount Moriah. Abraham pleaded with God to save him and his son, for “if we drown, who will obey Your commandment, who will sanctify Your name?” God immediately dried up the water and Abraham and Isaac could proceed on their way.
A sin is like the river: it blocks a person’s path to God. However, the flowing water also has the positive value of sending the sins as far away as possible.