Our Sages of Blessed Memory have said, in [maseches] Arachin (15b): “Rabbi Yochanan said in the name of Rabbi Yosi ben Zimrah, all who speak Lashon HaRa are considered as if [they] deny HaShem, as it says “for they have said, ‘with our tongues we shall be strengthened, our lips are with us, who is our Master?’” (Tehillim: 12; 5) The reason [that Lashon HaRa is tantamount to denial of HaShem] follows that which [our Sages of Blessed Memory have] written in Sifrei Yirayim, for it is known, that one who wishes to speak Lashon HaRa, looks to all of his sides, [for] perhaps that man, [he being the target of his Lashon HaRa], is standing [in his vicinity. Consequently, by speaking in such a manner, the speaker of Lashon HaRa acts as if] The Eye Above, [in Heaven], does not see, Heaven Forbid. [The above] resembles that which our Sages of Blessed Memory have said [in maseches “Bava Kamma” (79b)] concerning the thief. [The following teaching is taken from] Midrash Tanchuma: “Lashon HaRa is [such a] severe [transgression], for a person does not emit [the slander] from his mouth until he denies HaShem, as it says, “for they have said, [‘with our tongues we shall be strengthened, our lips are with us, who is our Master?’”].”
Therefore, [in light of the above, those] who have a brain in [their] skull will always see to motivate himself to fight the war of HaShem against his evil inclination, so that he should not be ensnared in this great and bitter sin [of Lashon HaRa. Once the person fights the war of HaShem successfully against the Yetzer HaRa], then praiseworthy is [that person's] portion, [both] in this world and in The World to Come.
 “Kofer” is one who denies HaShem, the whole Torah, or any part of the Torah.
 This teaching is found in the Midrash Rabbah on Parshas Metzora (16; 1).
 ‘Torah’ means ‘law’. In our context, the term ‘Torah’ is written in light of the connection between the sin of Lashon HaRa and violation of the entire Torah.
 Tzara'as is a form of affliction that can affect ones home, clothing, or person. The affliction can manifest in many forms and often resembles the appearance of leprosy. This Divine Punishment can come about as a consequence of several types of sins, including Lashon HaRa.
 “Metzora” refers to the individual afflicted with tzara'as.
 “Metzora” is one with a spiritual affliction, somewhat similar to leprosy – מצורע (Metzora) can also be read as a shortened version of the words "מוציא רע" as in "מוציא שם רע" (Motzi Shem Ra) – one who brings out an evil name by speaking slanderously concerning a person. "מוציא שם רע" usually refers to one who speaks libelously against another.
 Since the word “metzora” is similar to “Motzi Shem Ra”. Therefore, since it mentions the word "Torah" five times, (in varying forms), in the section of the Torah discussing the metzora, we can learn from here that one who speaks “Motzi Shem Ra” - “libel”, is considered as if he has transgressed the Five Books of The Torah.
 For this teaching, also see in “Reishis Chochmah”, The Gate of Holiness, Chapter 13, paragraph 3.
 “The Eye Above” refers to “the Eye” of HaShem.
 The gemara notes in the name of Rabbi Yochanan that the Torah is stricter concerning the thief than the robber, for the thief is afraid to act in front of people, though he behaves as if HaShem does not know what he is doing. The thief is worse than the robber, for the robber treats the honor of the servant (people) equal to the honor of his Creator (HaShem). However, the thief respects people more than he respects HaShem, as he wouldn’t dare steal in the presence of people, though acts as if “no one is watching” when there are no people around, thus acting as if HaShem is unaware of his actions. Rabban Gamliel compares the thief to one who invites all of the townspeople to a party, while failing to invite the princes. In contrast, the robber is compared to one who has a party and does not invite the townspeople and the princes. The one who invited the townspeople and declined to invite the princes would suffer a worse punishment. So too, the thief, by sinning and ignoring HaShem, while he takes notice of people when committing his crimes, is considered worse than the robber.
 This teaching from Midrash Tanchuma is found on Parshas Bereishis, siman 8, Parshas Metzora, siman 2.