from the writings of Rabbi Sholom DovBer Schneersohn of Lubavitch [the Rebbe Rashab]
On account of our many transgressions, the sin of baseless hatred is found especially among pious people. Each builds himself a pedestal based on his own exclusive conception of Torah scholarship and avodah. There is neither bond nor unity between them. In truth, it is of fundamental importance for those who are occupied in Torah and in the service of G-d to join together and communicate with each other; for regarding the study of Torah our Sages applied the verse "Just as iron sharpens iron, so does one man sharpen another." Just as one iron sharpens the other, two sages sharpen each other in Halachah.
No person can assume (on his own) that his own perspective is valid. Only when one hears a colleague's opinion and each dialectically debates with another seriously, is it possible to arrive at a true view of the matter at hand.
Similarly in avodah (the service of worship and personal development), when people reveal and speak about their inner faults to each other, a number of benefits can be attained. For one thing, each person has certain faults of which he is not aware, for his own self-love [as the verse declares [Mishlei 10:12] "Love covers all faults"]. This surely applies to one's shortcomings with regard to various character traits. One's innate self-love masks them, and another person will help him by bringing them to his attention.
Furthermore, when a person reveals his inner faults he feels greater remorse than he felt before speaking. This stronger sense of regret over all past faults (leads him to totally) uproot his desire for them, thereby correcting his soul considerably. The confession of sins must be verbal. This corrects the soul of the sinner to a great degree, for the verbalization of one's sin strikes the innermost chords of his soul, causing him to feel great pain and regret.
Our Sages explained [Yoma 75a] a similar concept in their commentary on the verse [Mishlei 12:25] "Worry in the heart bows it down". The Hebrew verb ישׁחנה suggests a similar verb ישׁיחנה , meaning "speak of it". Thus the verse can be interpreted to mean "If there is worry in the heart of man, let him tell others (about it)". At the time one talks about his troubles, his pain becomes greater, but afterwards he feels better. Similarly in avodah, when one talks about one's inner faults, he feels greater pain at the time, but afterwards he feels better, for many flaws and sins have thereby been removed.
Furthermore, when people discuss spiritual improvement, each one proposes means of correcting flaws, and they can jointly resolve to correct certain aspects of their behaviour. A resolution reached by two or more people is more lasting than a resolution made by one person alone. Thus, it is obvious that many benefits result when those who serve G-d combine their efforts.
Now, this is only possible if one possesses the quality of bittul (selflessness) and is capable of coming close and becoming one with another person. But if one is dominated by yeshus (self-concern), it is impossible for him to reveal his inner faults to someone else. If he has a low opinion of others, how can he reveal his affairs to him, and what purpose will it serve? How could another person benefit him?
The fundamental reason however, for this attitude, is that he cannot become one with someone else, for in Torah study he stubbornly defends his opinion and thinks that his wisdom and knowledge is truth. He refuses to accept another opinion, or even consider it impartially without prejudice. When people discuss an idea in this manner, they draw further apart and become opponents. This disagreement in turn becomes a reason for preventing future co-operation and joining together, (for "he said such-and-such", and so on.)
Similarly, in avodah, such an attitude prevents cooperation and unity. One will not value the Divine service of another person or consider him to be an oved (one who devotes himself earnestly to Divine service through worship and self-refinement). He will minimize the worth of the other person's service and scorn and negate his positive qualities.
When he sees that another person possesses a fault - albeit a superficial one which does not at all affect the main body of his service - he will magnify it, speaking about it often, and humiliating him. Should he discover a character flaw in his fellow, (which is inevitable) for "who is so righteous as to have no flaws?" - he will say that this flaw proves that any good his fellow possesses is really of no consequence. He will exaggerate the evil to the point where any good the person possesses will be unnoticeable.
This is simply not true, for that individual's Divine service in prayer, Torah study and the fulfillment of mitzvot is in itself good, and constitutes his primary labour throughout the day. The negative character trait he possesses is merely one not yet corrected. "Man is born like a wild young donkey." [Iyov 11:12] He is born in an unrefined state and he must strive to correct his character traits throughout his entire life.
This service is alluded to in the verse "The days of our years - there are seventy years in them". The Hebrew word for "in them" בהם is spelled almost the same as the word for "animal" בהמה. A person is given seventy years in which to refine the seven evil character traits of his animal soul. This process of self-correction cannot be completed at once, rather [Shmos 23:30] "little by little will I drive (the heathern Canaanites) out from before you", i.e. considerable effort is called for. Only after extensive endeavours in prayer, meditation on G-dliness, and strengthening of the attributes of one's G-dly soul, is it possible to weaken, refine and purify, the natural emotions of the animal soul. And since the abovementioned individual serves G-d, he will surely refine and correct his character traits.
At times one needs help from others in order to achieve this goal, for one's own self-love will sometimes blind him from recognizing a negative character trait. A friend can make him aware of this fault and advise him on how to correct it. If one really loves another person, he will do so privately. If instead he dismisses him, scorns him, and humiliates him - particularly if he does so in public - this is a clear sign that he hates him and does not seek his good. (Nor does he genuinely want what every individual should desire - the service of G-d within the world, for this is G-d's will and desire).
The reason for this behaviour is his own lack of service; his own service is not sincere. Although he serves G-d in prayer and in study, he is not sincere, since he lacks bittul and selflessness, possessed as he is by yeshus and self-concern.
Source: "On Ahavas Yisrael - Heichaltzu" - A Chassidic Discourse by Rabbi Sholom DovBer Schneersohn of Lubavitch - Kehot Publications