Moussar sur Le Deutéronome 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.

And he who does not guard himself from everything that destroys his body, finds that he is an enemy to himself, seeks his own evil, and will be judged [for it]. For if one harms others, the sin is in his hands, and how much more so if he injures himself. And “he who troubles his own flesh is cruel”(Proverbs 11:17). And even more so one needs to guard himself from a place which has even the slightest risk of mortal danger. And if he enters a dangerous place for money, it turns out that his wealth is dearer to him than his life, and if a miracle is performed for him, it depletes his merits. And it turns out that he sells his merits and great goodness stored up for him in the world to come, exchanging the reward of mitzvot for money, which perishes and is destroyed. Further, he will surely be punished. And he is liable [to forfeit] his life as the words of the Merciful One warned: “Guard yourself and guard your body greatly (Deuteronomy 4:9), and guard your souls greatly (Deuteronomy 4:15)”. Therefore, no man should go to a dangerous place, such as on dangerous roads or through seas and rivers, unless it is absolutely necessary for his livelihood. And [in these cases] he should bring with him armed men in order to minimize the danger through natural means. And if he can go on dry land, he should not go by river or sea, which increase the danger. And proportional to the danger, one loses merit if a miracle is performed. And therefore all that one is able to do to minimize danger with money or extra effort, behold, such a person [who does this things] is zealous and will be rewarded, and the reward is greater than the expenditure. And the commandment to take utmost care of yourselves which he fulfills is sufficient to save him from all distresses and bring blessings upon his home. And he will remain intact in his body and intact in his wealth (and more is written on this in the section titled “Guarding”).