"Rabbi Yochanon asked his students, 'What is the straightforward path to which a person should cleave?' Rabbi Eliezer said, 'A good eye.' Rabbi Yehoshuah said, 'A good friend.' Rabbi Yosi said, 'A good neighbor.' Rabbi Shimon said, 'Know the consequences of your deed.' Rabbi Elazar said, 'A good heart.' Rabbi Yochanon said, 'I see the words of Rabbi Elazar, 'A good heart,' encompasses of all your words.' (Pirkei Avot 2:8)"
What is the essence of a good heart? The true meaning of "a good heart" is the golden attribute of acceptance, as personified in one who always holds his patience. He is never short-tempered, keeps himself far from anger, and always answers with a gentle response. Moreover, he is kind and generous to his friends, neighbors, and the entire world.
The core of morality is perfect patience. A person who keeps calm in every circumstance treats other people fairly, respectfully, and affectionately.
Envision being in the presence of the saintly Rabbi Yisrael Salanter. Perceive his good heart, emanating with patience, inner calm, and sweet character traits. Note how he treats every person with dignity, care, and sensitivity. He shows patience with others, even in trying situations. Feel the joy, inspiration, and positive influence of being in his presence.
(Based on the commentary of Rabenu Yona)