It is known that the greatest of all mitzvos is the [mitzvah of involvement in] Torah [study], and, in contrast, idle chatter and [words of] mockery [can be classified among the greatest of sins] for [these sins] are the opposite the [mitzvah of] Torah study. This being the case that forbidden speech is the worst of all sins, the individual who involves himself in such sins] derives [a] greater [degree of] pleasure through [involvement in] idle chatter and [words of] mockery than from [any] of the [other sins. The person who involves himself in such sins derives such a great degree of pleasure] though [he doesn’t receive any true benefit from such sins, even] in this world. This is the case that the sinner experiences such great pleasure though he truly does not attain any benefit for his having sinned], since the Spirit of Impurity is exceedingly great. [The Spirit of Impurity is exceedingly great to the extent that it is] analogous to a flowing spring [of impurity, in] contrast [to] The Torah which is comparable to a flowing spring [of that which is holy and pure].”
It is known that the Spirit of Impurity that is created through [the performance of] the [given] sin is itself that which metes out punishment [to the] person in gehinnom, after his passing. [In reference] to [the above teaching], our Sages of Blessed Memory, have [utilized] the phrase “נופל בּגיהנם” – “fall into gehinnom”, [in order] to teach us, that at the time [that one] says [words of] mockery, the great Spirit of Impurity flies upon him, as mentioned above, and [it is] precisely he himself [who] is falling* into gehinnom, during his lifetime, may The Merciful One save us [from such things. The above teaching relates to that which is taught] in “Nefesh HaChaim”, Gate 1, Chapter 12. One could also say that his second [teaching] is similar to [the above teaching. However], now is not the place to go [on] at length [by quoting these teachings from sefer “Nefesh HaChaim”].
 “Aveirah” is a sin.
 From here we can see how one mitzvah leads to another mitzvah and one aveirah leads to another aveirah, for when the person habituates himself to perform a given mitzvah, he will have an urge to perform that mitzvah until he has performed that mitzvah. The same is true of a given aveirah that one may be accustomed to perform. The person could be troubled by the Spirit of Impurity until he performs that given aveirah, receiving “relief” from that Spirit once he sins. From the above we can truly appreciate the importance and great benefit of becoming accustomed to perform mitzvos, even though it may be more challenging initially to perform those mitzvos. Similarly, as the performance of aveiros, especially with regularity, as we learn in “Pirkei Avos”, makes one more inclined to perform the given aveiros, it is essential that the person make a strong effort, if necessary, to overcome to Spirit of Impurity and not fall prey to the Yetzer HaRa by performing the given sin. HaShem has endowed within each of us the power of free-will and the ability to overcome our base desires and ignore the council of the Yetzer HaRa. This follows that which HaShem told Kayin before he murdered Hevel, his brother: “…and Kayin was exceedingly angry and he was crestfallen. And HaShem said to Kayin, ‘Why are you angered and why are you crestafallen?’ Is it not that if you improve your actions you will be forgiven for your sin and if you do not improve your actions in this world, on the Great Day of Judgment your sin awaits and sin crouches on the entrance of your heart and you have been given the control over the Yetzer HaRa and you are the desire [of the Yetzer HaRa] and you shall rule over it, whether to act meritoriously or to sin.” (B’reishis: 4; 6 – 7) Translation of the second pasuk is taken from the commentary Yonasan ben Uziel.
We see from the above of the ability of the person to overcome their Yetzer HaRa and therefore, if they choose not to do so, they could be held accountable on the Day of Judgment, unless they properly perform teshuvah.
RaSh”I on maseches “Kiddushin” (30b) explains in reference to the above quoted pasuk (B’reishis: 4; 7), that if the individual improves by choosing that which is good, then that person will be raised above his Yetzer HaRa. We can see that, as a result of choosing to perform a mitzvah or any other good action, the person is effectively strengthening themselves over their Yetzer HaRa and being further elevated above it. Kayin chose to follow the dictates of his Yetzer HaRa and murdered his brother, Hevel. As a result of this great sin, Kayin was greatly punished by HaShem. After HaShem told Kayin of his punishment, Kayin recognized the severity of his action and said, “…My sin is too great to bear”. (B’reishis: 4; 13) The word “שׂא” – “sa” is translated as “elevated” in the context of HaShem telling Kayin how he can elevate himself above his Yetzer HaRa – “הלוֹא אם תיטיב שאת...” – “Is it not that if you improve your actions, you will be elevated [above your Yetzer HaRa]…”. (B’reishis: 4; 7) The word with the root שׂא” – “sa” is similarly used in by Kayin when he recognized that his sin of murdering Hevel was so severe. After subjecting himself to the will of the Yetzer HaRa by murdering Hevel, Kayin states, “ ...גדוֹל עוֹני מנשוֹא” – “…My sin is too great to bear”. (B’reishis: 4; 13) From here we see that by overcoming the Yetzer HaRa, the person can elevate themselves, while, in contrast, if the person follows the dictates and inclination of his Yetzer HaRa, their sin can be “too great to bear”, chas v’shalom.
 The sins of idle chatter and mockery are considered to be the worst of sins, for, as the Chofetz Chaim explained previously, forbidden speech involves the use of one’s power of speech for that which is forbidden, in contrast to Torah learning which employs the power of speech for the positive. The reason why the power of speech is so powerful, both for the good and for the bad, is that it is an action which is spiritual in nature, only involving the voice, as the Chofetz Chaim explained in the end of chapter one of “Sha’ar HaZechirah” – 13th of Tishrei.
 This teaching of ChaZa”L that the Chofetz Chaim refers to, concerning the mocker who is “falling into gehinnom”, is found in maseches “Avodah Zara” (18b), quoted in the name of Rabbi Shimon ben Lakish.
The teaching from the gemara states as follows:
“Rabbi Shimon ben Lakish said: ‘All of those who mock fall into gehinnom, as it says [in sefer “Mishlei”], “The haughty sinner’s name is “לץ” – “mocker”, he acts with – “עברה” – “evrah” - wrathful sin.” (21; 24), “evrah” only referring to gehinnom, as it says [in “Tzifaniah”], “That day is a day of - “evrah” – wrath…” (1; 15)
 *Chofetz Chaim’s note: [The term “נופל” – “falling” – is related to the word “residing”, as we see concerning the death of Yishmael, the son of Avraham, as follows]: “…upon the countenance of all of his brothers he fell – “נפל”.” (B’reishis: 25; 18)
The Chofetz Chaim is pointing out that when we are taught that the person who speaks words of mockery is falling into gehinnom during his liftetime, we are being taught that at the time that the person speaks words of mockery, he is, in effect, causing himself to, at that moment, reside in gehinnom, as the Spirit of Impurity over him at the moment of his sin.
 Rav Chaim Volozhin, the author of “Nefesh HaChaim”, in addition to teaching that which the Chofetz Chaim copied in sefer “Shmiras HaLashon”, notes that when the gemara teaches that “the evildoers deepen gehinnom for themselves (Eruvin, 19a), it means that through their actions, the evildoers make gehinnom deeper and wider for themselves. (See sefer “Yishayahu” (50; 11) in this context).