Another matter, “then Moses…sang” – that is what is written: “Your lips drip nectar, [my bride]” (Song of Songs 4:11). Moses said to the Holy One blessed be He: ‘Master of the universe, with what I sinned before You, I laud You.’ Rabbi Levi bar Ḥiya said: This is analogous to a province that rebelled against the king. The king said to his duke: ‘Let us go and wage war against it.’
The duke said to him: ‘You are unable [to conquer it].’ The king was silent and went himself at night and conquered it. The duke knew, and he crafted a crown and brought it to the king. [The king] said to him: ‘What is the reason for this crown?’ He said: ‘It is because I sinned in this regard and said that you were unable.’
So too, Moses said before the Holy One blessed be He: ‘I know that I sinned before you with the word az, as it is stated: “Since [me’az] I came to Pharaoh [to speak in Your name he has harmed this people, and You did not rescue Your people]” (Exodus 5:23), and you drowned him in the sea. That is why I am praising you with the word az; that is what is written: “Then [az] Moses…sang.”’ Come and see the path of the righteous, with that with which they sin and they atone; that is: “Your lips drip nectar, my bride.”
From whom do they learn this? It is from the Holy One blessed be He, as with that that He strikes, He heals, as it is stated: “For I will restore health to you, and I will heal you of your wounds” (Jeremiah 30:17); with the wounds that I smite you, I heal you.3The phrase “of your wounds” may also be translated “with your wounds.” The midrash interprets the verse to mean that God says: I will use your wounds themselves to heal you.
From where is it derived? Know that it is so from the Holy One blessed be He. Come and learn from [what happened with the waters of] Mara. He indicated a bitter item to Moses, [Moses] cast it in the water, and the water was made sweet, as it is stated: “The Lord showed him a tree and he cast it into the water” (Exodus 15:25).
Which [tree] was it? Rabbi Natan says: It was oleander. Rabbi Yehoshua says: It was a willow. Rabbi Eliezer HaModa’i says: It was an olive tree.
In any case, it was a bitter tree and it sweetened the bitter water. So too, Moses complained only with az, and with what he sinned, he atoned, and said: “Then [az] Moses…sang.”