As Pharaoh continues to resist Moses’ demand to let the people Israel go free, God introduces additional and more intensive demonstrations of power. The Nile River, the single most important natural resource of the kingdom, is now targeted for attention. The lifeblood of Egypt will now be turned literally into blood. Pharaoh and his people could not ignore the impact of this catastrophe. The God of the Hebrews had power over Egypt’s greatest resource. To accomplish this plague God instructs Moses to tell Aaron to stretch out Moses’ staff over the waters of Egypt (Exodus 7:19). How odd that Moses was not to perform this act himself. That is, until the midrash (Exodus Rabbah 9:10) gives an instructive explanation.
Moses was saved from certain death when, as an infant, his mother sent him adrift on the Nile in a basket. The midrash, however, assigns Moses’ salvation to the waters of the Nile rather than to the prescience of his mother. To God, it would be an act of supreme ingratitude for Moses to afflict the very waters that saved him. Hence, Aaron had to be the one to do the deed.
The Rabbis attached great importance to the value of gratitude which they termed “hakkarat ha-tov,” meaning, recognizing the good. Ethicists refer to this same value as reciprocal kindness. Should you benefit from an act of kindness shown you by another, you have an obligation to return the favor. Were Moses to effect the plague of blood on the Nile he would be violating the principle.
Here we have a fine example of how the process of interpretation reveals values as much as it clarifies the text.