מדרש אויף מלכים ב 2:21

R. Shimon b. Gamliel says: Come and see how different are the ways of the Holy One Blessed be He from the ways of flesh and blood. (A man of) flesh and blood heals bitter with sweet, but the Holy One Blessed be He heals bitter with bitter. How so? He places something damaging into something that has been damaged so that a miracle be wrought in it, as in (Isaiah 38:21) "And Isaiah said: Let them take a cake of figs and apply it to the rash and he will recover." Now does not raw flesh, when you apply a cake of figs to it, become putrid? (The resolution:) Place something damaging into something that has been damaged so that a miracle be wrought in it. Similarly, (II Kings 2:21) "And he went to the (polluted) spring and threw salt into it, etc." Now does not even fresh water become putrid when salt is put into it? (The resolution:) Place something damaging, etc. The expounders of metaphors said: He showed him (Moses) words of Torah, which are compared to a tree, viz. (Mishlei 3:18) "It (Torah) is a tree of life to those who hold fast to it, etc." It is not written "Vayarehu etz" ("And He showed him a tree"), but "Vayorehu" ("And He taught him"), as in (Mishlei 4:4) "Vayoreni ('And He taught me') and He said to me: Let My words (of Torah) sustain your heart."

Another interpretation (of Exod. 15:25): AND THE LORD SHOWED HIM A TREE. What was it?⁶¹Tanh., Exod. 4:24; Mekhilta de Rabbi Ishmael, Wayassa‘ 1; Exod. R. 50:3. R. Joshua says: It was an olive tree; R. Nehemiah says: A willow tree. Some say: The roots of a fig tree; and others say: The roots of a pomegranate, since there is nothing as bitter as those. But the sages say: It was ivy⁶²Gk.: rhododaphne (“rose laurel” or perhaps “rhododendron”). wood, and there is nothing as bitter as that. R. Ishmael the son of R. Johanan ben Baroqah said: See how great are the miracles of the Holy One! <Those of> flesh and blood cure the bitter with the sweet, but the Holy One cures the bitter with the bitter.⁶³See below, Exod. 10:9, and the note there. Thus it is stated (in Jer. 30:17): [FOR I WILL RESTORE HEALTH TO YOU]: AND I WILL HEAL YOU OF YOUR WOUNDS, SAYS THE LORD. By whatever means he wounds he heals. The Holy One told Moses to put something sour into something sour for it to become sweet thereby. Similarly it is written (in II Kings 2:21): SO <ELISHA> WENT OUT TO THE SPRING OF WATER, THREW SALT IN IT,…⁶⁴The biblical text indicates that there is no lacuna here. AND SAID: THUS SAYS THE LORD: I HAVE HEALED <THIS> WATER. Similarly (in Is. 38:21): AND ISAIAH SAID: LET THEM TAKE A CAKE OF FIGS <AND APPLY IT TO THE BOIL, AND HE WILL LIVE>. Is it not a fact that, when one puts fig juice on the flesh, it is immediately consumed? <This exception,> however, <was> in order to perform a miracle.

What kind of tree was it? R. Joshua held: It was a willow tree. R. Nathan declared: It was a bitter ivy tree, while R. Eleazar of Modi’im insisted: It was an olive tree. R. Joshua the son of Karha maintained that it was a cedar tree. Others said that it was the root of a fig tree and the root of a pomegranate tree. In any case, it was extremely bitter. R. Simeon the son of Gamliel said: Come and observe how different the ways of the Holy One, blessed be He, are from the ways of man. Man improves the taste of a bitter thing with something sweet, but the Holy One, blessed be He, improves the taste of a bitter thing by adding something bitter. How does He do that? He places something that causes damage into a thing that is damaged and thereby performs a miracle. For example, And Isaiah said: Let them take a cake of figs and lay it for a plaster on the boil, and he shall recover (Isa. 38:21). Is it not a fact that if you place a cake of figs on a raw piece of flesh, the flesh will decay immediately? This verse illustrates that He places a thing that injures upon something that was injured in order to perform a miracle. Similarly, And he went forth unto the spring of the waters and cast salt therein, and said: “Thus saith the Lord: I have healed these waters; there shall not be from thence anymore death or miscarrying” (II Kings 2:21). Is it not a fact that sweet water into which you put salt water is spoiled immediately? But here He placed a thing that is distasteful into something that was distasteful, and thus performed a miracle thereby. The Holy One, blessed be He, declared unto Moses: Is it not a fact that I am a unique craftsman? Do I not heal with what I wound? If these waters are bitter, I will make them palatable by adding something that is bitter.