Chapter thirty of the Tanya instructs: "Be humble of spirit before every person" (Avot 4:10)—and it means every person, including the worst person you can imagine.
How is this possible? The Tanya's answer: "Do not judge your fellow until you have stood in his place" (Avot 2:4). The person who sins flagrantly may be in a situation you cannot fathom. His livelihood forces him into the marketplace all day, surrounded by temptation. His eyes see what your eyes have never seen. His evil inclination may burn like a baker's oven—a level of desire you have never experienced.
Rabbi Schneur Zalman is not excusing the sinner. He says explicitly that even such a person is still called "an utter evildoer" because he should have controlled himself despite the difficulty. Fear of God—knowing that God sees every action—should have been enough to restrain him. But—and this is the crucial pivot—the question is not whether he is wicked. The question is whether you have the right to feel superior.
The Tanya says: if you spend your days in study and rarely face severe temptation, your righteousness may be easier than his struggle. The person who battles a raging fire of desire and loses is still a more intense spiritual combatant than the person who never faced the fire at all. "Each person according to his place and rank" must examine whether his service of God is proportional to the difficulty of his personal test.
This teaching generates a paradox that the Tanya embraces: genuine humility before every person is compatible with recognizing that the other person may be wicked. You are not pretending that sin is acceptable. You are admitting that if you had that person's temperament, that person's circumstances, that person's level of temptation, you might have done worse. The comparison destroys arrogance without destroying moral standards.
This also a person must resolve in his heart to fulfill the instruction of our Rabbis, of blessed memory, “And be humble of spirit before every person.”1 Avot 4:10. This you must be in true sincerity, in the presence of any individual, even in the presence of the most worthless of worthless men. This accords with the instruction of our Sages, “Do not judge your fellow man until you have stood in his place.”2 Ibid., 2:4. For it is his “place” that causes him to sin, because his livelihood requires him to go to the market for the whole day and to be one of those who “sit at the [street] corners,” where his eyes behold all the temptations; the eye sees and the heart desires,3 Rashi, Numbers 15:39; Bamidbar Rabbah, 10:2. and his evil nature is kindled like a baker’s red-hot oven, as is written in Hosea, “He burns like a flaming fire….”4 Hosea 7:6. It is different, however, with him who goes but little to the marketplace and who remains in his house for the greater part of the day; or even if he spends the whole day in the market but is possibly not so passionate by nature—for the evil inclination of all people is not the same: there is one whose nature…,5 For more on this subject, see, e.g., Likkutei Torah, Vayikra 2d; Va’etchanan 5a. as is explained elsewhere. In truth, however, even he whose nature is extremely passionate and whose livelihood obliges him to sit all day at the [street] corners has no excuse whatsoever for his sins, and he is termed an utter evildoer (rasha gamur) because there is no dread of G–d before his eyes. For he should have controlled himself and restrained the impulse of his desire in his heart because of the fear of G–d Who sees all actions, as has been explained above,6 Chs. 12, 19. for the mind has supremacy over the heart by nature. It is indeed a great and fierce struggle to break one’s passion, which burns like a fiery flame, through fear of G–d; it is like an actual test. Therefore, each person according to his place and rank in the service of G–d must weigh and examine his position as to whether he is serving G–d in a manner commensurate with the dimensions of such a fierce battle and test—in the realm of “do good,”7 Psalms 34:15. That of “turn away from evil” will follow later. as, for example, in the service of prayer with kavanah (devotion), pouring out his soul before G–d with his entire strength, to the point of exhaustion of the soul,8 Sifrei on Deuteronomy 6:5—עד מיצוי הנפש—literally, to the extent of “wringing out” the soul. while waging war against his body and animal soul within it which impede his devotion, a strenuous war to beat and grind them like dust, each day before the morning and evening prayers. Also during prayer he needs to exert himself, with the exertion of the spirit and of the flesh, as will be explained later at length.9 Ch. 42. Anyone who has not reached this standard of waging such strenuous war against his body has not yet measured up to the quality and dimension of the war waged by one’s evil nature which burns like a fiery flame, that it be humbled and broken by dread of G–d. So, too, in the matter of Grace after meals and all benedictions, whether those connected with the partaking of food or with the performance of precepts, [to be recited] with kavanah, to say nothing of the kavanah of precepts “for their own sake.” So, too, in the matter of one’s occupation in the study of the Torah, to learn much more than his innate or accustomed desire, and inclination, by virtue of a strenuous struggle with his body. For to study a fraction more than is one’s wont is but a small tussle which neither parallels nor bears comparison with the war of one’s evil impulse burning like fire, he is called utterly wicked (rasha gamur) if he does not conquer his impulse so that it be subdued and crushed before G–d. For, what difference is there between the category of “turn away from evil” and that of “do good”?10 Sins of omission are as reprehensible as sins of commission insofar as disobedience is concerned. Both are the command of the Holy King, the One and Only, blessed is He. So, too, with the other commandments, especially in matters involving money, as the service of charity (tzedakah) and the like. Even in the category of “turn away from evil,” every intelligent person can discover within himself that he does not turn aside from evil completely and in every respect where a hard battle at a level such as described above is called for, or even on a lesser level than the aforementioned: for example, to stop in the middle of a pleasant gossip, or in the middle of a tale discrediting his fellow, even though it be a very small slur, and even though it be true, and even when the purpose is to exonerate oneself—as is known from what Rabbi Simeon said to his father, our saintly teacher, “I did not write it, but Judah the tailor wrote it,” when his father replied, “Keep away from slander.” [Note there, in the Gemara, beginning of ch.10 of Bava Batra.]11 Bava Batra 164b. The same applies to very many similar things which occur frequently, especially with regard to sanctifying oneself in permissible things, an enactment based on the Biblical text, “You shall be holy…”12 Leviticus 19:2. and “Sanctify yourselves….”13 Leviticus 20:7. Moreover, “Rabbinic enactments are even stricter than Biblical enactments,”14 Eruvin 21b; Mishnah, Sanhedrin 11:3. Berachot 3b; Avodah Zarah 41a; See also Rosh Hashanah 19a; Taanit 17b; Yevamot 85b. and so forth. But all these and similar ones are of the sins which a person tramples underfoot and has come to regard as permissible in consequence of repeated transgression, and so on.15 Avodah Zarah 18a. In truth, however, if he is a scholar and upholds the Law of G–d and wishes to be close to G–d, his sin is very great and his guilt is increased manifold in that he does not wage war and does not overcome his impulse in a manner commensurate with the quality and nature of the intense battle mentioned above, than the guilt of the most worthless of worthless men of the corner-squatters who are removed from G–d and His Torah, whose guilt is not as heinous—in not restraining their impulse which burns like a fiery flame by means of the dread of G–d, Who knows and sees all their deeds—as the guilt of the person who is ever so close to G–d, His Torah, and His service. As the Rabbis, of blessed memory, said about Acher, “For he knew My glory….”16 Eyn Yaakov, Chagigah 15a. (Comp. Hagahot HaBach 4, ad loc.) Therefore the Rabbis declared in regard to the illiterate that “deliberate infringements [of the Law] are regarded, in their case, as inadvertent acts.”17 Bava Metzia 33b.