When we are focused on the body and its needs, it is impossible to love others without personal interest, because each individual has his own separate body. But if our principal focus is upon the divine soul, i.e., the divine spark within each of us, it is possible to truly love another, because souls are all connected to one another at their source.

We can come to love others by recognizing the centrality of the divine soul in each individual:

By realizing the things mentioned above, when one’s body is despicable and abhorrent to him, and his joy is only the joy of the soul, this is the direct and simple way to fulfill the mitzva of “You shall love your fellow as yourself,” with regard to every Jewish soul, great and small.

Bodies are distinct and different from one another, but souls are all connected:

Because his body is abhorrent and disgusting to him, whereas with regard to the soul and spirit, who can know the level of their greatness, as their root and source come from the living God. Additionally, all souls complement one another and have one Father, and therefore the Jewish people are called “brothers,” as the source of their souls is from the one God, and only their bodies are separate. Therefore, those who consider their bodies to be the most important thing, and their souls to be secondary, cannot have true love and brotherhood between them; rather, their love is dependent on something [i.e., self-interest]. (Rabbi Shneur Zalman of Liadi, Tanya, Likutei Amarim 32)

Further reading: For more on the source of the soul, see p. 223.

We are all well aware of our own faults, but we are not distressed by them, because we love ourselves. Nevertheless, when another person points out our faults, we become angry, as he has emphasized our shortcomings and made them into an issue. The mitzva of “you shall love your fellow as yourself” instructs us to relate to the shortcomings of others as we do to our own, i.e., our love for another individual must not be diminished as a result of his shortcomings.

Due to self-love, we do not consider our shortcomings as serious:

Just as “a person does not find fault in himself” (Shabbat 119a) does not mean that he does not know his faults (on the contrary, he is able to perceive the extent of his deficiencies better than anyone else, as another person sees him with his eyes alone, whereas he can see into his own heart); rather, the meaning is that he does not consider his faults significant enough to become provoked by them. It is as though he does not see them. The tremendous love that he has for himself covers up all the sins he is aware of.

Why we become angry when another person exposes our shortcomings:

When another person perceives and understands one of his faults, he becomes exceedingly angry, even though he knows that it is the truth. The primary anger is not over the deficiency itself, as if his fellow has imagined something false, since he knows that it is in fact true. It is because his associate’s knowledge of his deficiency makes it substantial and activating. This was not the case when [only] he knew of it, as love covered it up. He is angry at his associate for exposing his fault and bringing it out of concealment. It had been covered up by love such that it was completely invisible, and now, with regard to his fellow, it is visible, as something of substance.

As a result of our love of others, we should not make an issue of their shortcomings:

This is the explanation of (Shabbat 31a): “That which is hateful to you,” i.e., the exposure [of your faults], “do not do to another.” Do not see his faults and sins…as something of substance. Rather, your love for him should be so great that it covers up his sins. Do not react as a result of your knowledge of these sins. This is like when one has great passion for another person and is powerfully drawn to that person from the very essence of his soul. He does not acknowledge anything wicked that the person does to him that obstructs his love; such actions are like nothing to him when compared with the strength of his love. (Tzemaĥ Tzedek, Derekh Mitzvotekha 28a)