Midrash su Geremia 23:29

Raba said again: "A young scholar is like a seed lying under a hard clod which, when it has once sprouted, grows fat." Raba also said: "If a young scholar gets angry, it is the [zeal for the] Torah that excites him, for it is said (Jer. 23, 29) Is not thus my word like the fire saith the Lord?" R. Ashi said: "A scholar who is not as firm as iron cannot be considered a scholar; for the end of that passage reads: And like a hammer that shivereth the rock. What you derive from that passage." remarked R. Abba unto R. Ashi, "we infer from the passage here: It is written (Deut. 8, 9) A land whose stones are iron. Do not read it, Ab'neha (its stones), but read it, Boneha (its builders)." "Even so," remarked Rabina, "a man should train himself to speak calmly without anger, as it is said (Ecc. 15, 10) And remove anger from thy heart."

Our Rabbis were taught: The evil inclination of a man is so wicked that it is called so even by its Creator (Gen. 8, 21) For the inclinaiion of man's heart is evil from his youth. R. Isaac said: "The [evil] inclination renews its fight upon man every day, as it is said (Gen. 6, 5) And that every inclination of the thought of his heart was only evil all day long." (Ib. b) R. Simon b. Lakish said: "The evil inclination of man renews its fight upon man, and desires to slay him, as it is said (Ps. 37, 23) The wicked looketh out for the righteous, and seeketh to slay him; and were it not for the help of the Holy One, praised be He, man would not resist it, as it is said further: The Lord will not leave him in his hand, and will not condemn him when he is judged." In the college of R. Ishmael it was taught: My son, if that ugly (the tempter) meet thee, drag it into the house of learning (overcome it through study); if it is of stone it will be shattered; and if it is of iron it will be melted, as it is said (Jer. 23, 29) Is not thus my words like the fire? saith the Lord, and like a hammer that shattered the rock?

R. Chama b. Chanina said: "What is the meaning of the passage (Pr. 27, 17) Iron is sharpened by iron? It means just as iron sharpens another iron, so also when two scholars study together, one sharpens [the intellect of] the other." Rabba b. b. Chana said: "Why are the words of the Torah compared to fire? As it is written (Jer. 23, 29) Is not this my word like the fire? saith the Lord. They are to teach that just as fire cannot burn of itself [without having hold of an object], so the words of the Torah can also not remain with one who is alone." And this is also meant by R. Jose b. Chanina; for R. Jose b. Chanina said: "What is the meaning of the passage (Jer. 50, 36) The sword is against the lying soothsayers and they should become foolish. It means that the sword is against the learned who sit alone and study the Torah in privacy. Moreover, they become foolish; as it is said (No'alu) and they shall become foolish; nay, more, they will commit sins; for it is written here (V'noalu) and they shall become foolish, and it is written there (Num. 12, 11) Wherein we have acted foolishly (No'alnu), and wherein we have sinned; and if you wish I would conclude here from (Is. 19, 13) that The princess of Tzo'an are becoming fools (No'alu)."