Musar su Numeri 15:31

And there are many people among the masses who think that the main loss and damage to the soul is only from sins that [involve] an action; and that there is no losing of the soul for a man that is pure from sinning actively and who did not walk in the way of transgressions, but rather [only] prevented himself from doing [positive] commandments and good deeds. Therefore, we are obligated to make discernment known to the ones of a mistaken spirit. For our Rabbis, may their memory be blessed, said (Yerushalmi Chagigah 1:7), “The Holy One, blessed be He, forewent idolatry, etc., but He did not forego the sin of wasting [time available for] Torah [study].” And they said, (Sifre Devarim, Ekev), “Just like the reward for Torah study is greater than [that for] all of the commandments in the Torah, so too is the punishment for wasting [time for] it greater than [that for] all of the sins.” And they said (Sanhedrin 99a), “‘Because he has despised the word of the Lord and has breached His commandment’ (Numbers 15:31) - is stated about anyone for whom it is possible to engage in Torah [study] and does not engage [in it].” And we have already mentioned all of these to you in the Gate of the Torah (no longer extant).

Among the [negative commandments] that are dependent on the (heart) [tongue] are: “Since the Lord, your God, moves about in your camp to protect you and to deliver your enemies to you, let your camp be holy; let not anything unseemly be seen among you” (Deuteronomy 23:15). They, may their memory be blessed, said (Berakhot 25b) that included in this [prohibition] is that when we speak words of the Torah of God, may He be blessed - and in our speaking in prayer in front of Him - our camp should be holy, and let not anything unseemly be seen among us. Therefore we were commanded about this, to mention [God’s] name in holiness and to engage in words of Torah and prayer in holiness; and not to mention [God’s] name or words of Torah if he is naked or if there is a naked man across from him. And likewise were we warned that the place be clean, as it is stated (Deuteronomy 23:14), “you shall dig a hole with it and cover up your excrement.” And all the more so is he warned not to mention [God’s] name if his hands are not clean. And if his hands touched something disgusting to him, he should wash them - like the matter that is stated (Psalms 26:6), “I wash my palms in cleanliness.” And when one is walking on the path and he is in doubt if the path is clean, he should not mention [God’s] name, and he should not say words of Torah. And if there is something that is not clean behind him - such as excrement or a carcass or water [used for] soaking [flax] - one must move a distance of four ells away from where the odor ends; but in front of him, [the distance] is [as far as] his eye can see. And carefulness about this is one of the ways of fearing God, as it is stated (Malachi 3:16), “concerning those who revere the Lord and esteem His name.” And our Rabbis, may their memory be blessed, said (Berakhot 24b), “‘For he has shown contempt for the word of the Lord’ (Numbers 15:31) - this is [referring to] one who says words of Torah in filthy alleyways.” And our Rabbis, may their memory be blessed, said (Kohelet Rabbah 1:17), “‘He gives wisdom to the wise’ (Daniel 2:21) because the wise honor the Torah and occupy themselves with it in holiness.” But if He had given it to the silly, they would have said words of Torah in filthy alleyways.

And Rabbeinu Yonah has written in Iggereth Hatshuvah that "when men finish their work and their dealings and go to their houses or idle on the [street] corners or speak idle talk, their evil is very great and their sin exceedingly severe, for they [thereby] shame the Torah. For if they believed that there is no end to its reward, why would they not turn their feet to the house of study to learn? Does not a man rush to work knowing that all is vanity? And how can he forget the life of the world to come and not devote a day or an hour to learning? And let him not say: 'There is yet time to do for the L-rd, to learn Torah, and to occupy oneself with mitzvoth and tzedakoth.' He is guilty! He has sinned greatly against the L-rd! And Chazal have said on the verse (Bamidbar 15:31): 'For the word of the L-rd he has despised, and His commandments he has broken. Cut off shall be that soul; its transgression is in it,' that if it is possible for one to occupy himself with Torah but he does not do so, he shames the word of the L-rd. Therefore, every man is obligated to set aside a place in his house in which to learn halachoth or Scripture, each according to his ability. And when he is finished with his dealings or with his work, he must turn in there to study. And by doing so, he will "do wonders" for his soul, to rescue it from the pit. And he must reflect upon his end and consider his latter end, as Chazal have said: 'Consider three things and you will not come to transgression, etc.' And it is fitting that one find himself a pashut or a half [(types of coins)] to give charity for every day he fails to go to the house of study or to a place where he has one of the holy books to learn from."