Musar su Deuteronomio 4:9

And it [Torah] is the mainstay of the life of the soul, as we find in Sifrei, Parshath Ekev." R. Shimon says (Devarim 4:9): 'Only take heed to yourself and heed your soul exceedingly.' This may be compared to [the instance of] a king who captures a bird and hands it to his servant, saying to him: 'Take care of this bird for my son. If you lose it, do not think that you have lost a one-issar (a small-coin) bird, but that you have lost your soul.' And thus is it written (Devarim 32:47): 'For it [Torah] is not an empty thing for you [Not in vain do you toil in it; great reward inheres in it]; for it is your life.'"

I am surprised that when it comes to smallpox outbreaks, which spreads from child to child, why do people not take their children out of the city? In the future, the fathers will be responsible for the deaths of their children who are nursing, and have committed no sin, and those who are weaned and have committed no sins, and died from the sickness whose fathers did not take them away [from the city]. Every man who fears god should fear every eventuality. These things that are included in protecting the body are included in the warnings of (Devarim 4:9) 'take utmost care and watch yourselves scrupulously' and this is also the way of the world to take care of one's body since it is the container that the soul is wrapped up in so it will be a throne for the soul.

“Only observe for yourself, and guard your soul diligently, lest you forget the matters that your eyes saw” (Deuteronomy 4:9). And our Rabbis, may their memory be blessed, said (Menachot 99b) [that] anyone who forgets [even] one matter from his studies violates two negative commandments. Is it possible even if his studies were too hard for him? Hence we are taught to say, “And lest they depart from your heart” (Deuteronomy 4:9). The verse is only speaking of one who causes them to depart from his heart, by being idle from Torah study and not constantly poring over it.