Rabbi Yosef Yitzchak of Lubavitch, the Friediker Rebbe, writes:
In the winter of 5673 [1913] I went to visit my father, who was staying in Menton, France. Every day we would walk for hours along the seashore and I was privileged to hear of things which had never been told to anyone: practices, stories, visions and ideas of my holy ancestors, transmitted through the generations from rebbe to rebbe.
Father spoke much about "thinking chassidus" - meditating upon concepts of chassidic teaching - before prayer, while wrapped in tallis and tefillin. He discussed the topic continuously over the walks of several days and enumerated its many virtues. Thinking chassidus, he said, refines the body, making the mind and heart receptive to G-dliness. It repels the "animal soul", cleanses the "natural soul", subdues the "intellectual soul" and illuminates the world. It draws down a revelation of light in all worlds, from the highest to the lowest of levels. It transforms the essence of one's natural character, and illuminates the five levels of one's "Godly soul", nefesh, ruach, neshama, chaya and yechida.
All this applies to any individual who is involved in "the service of the heart" [i.e. prayer] and prepares properly for prayer, but how much more so to the perfectly righteous tzaddik. My father continued to describe at great length the heights attained by a tzaddik, concluding "one attains an appreciation of G-dly delight, ah Getleche ziskeit, a G-dly sweetness".
With G-d's help, I shall never forget that glorious moment, the sight of that holy face flaring in ecstasy as he enunciated the words "a G-dly sweetness". At that moment, I truly understood Rabbi Schneur Zalman's definition of a merkava [chariot] to the Almighty, those who "all their days... do not cease for a single moment to bind their minds and souls to the Master of the Universe".
To stroll within the splendorous natural surroundings of the Menton shore, and to be so immersed in G-dly delight, to so relish "G-dly sweetness" - this can only be an atzmi [a quintessential one; one who's every act, thought and character trait is utterly in line with and permeated by the very essence of his soul], a rebbe the son of a rebbe, a Jew of self-sacrifice, one for whom G-d is forever standing over him and the light of his soul is openly manifest within his being.
For a long time we walked along the shore without a word. All who met or passed us noticed the look of his holy face, shining with a G-dly light. Suddenly, as one who awakes from sleep, he turned to me and said:
"Yosef Yitzchok! Listen! All the benefits of thinking chassidus in tallis and tefillin prior to prayer, both for the ordinary chassid and for the tzaddik, are utterly insignificant compared to a single privilege: if the Almighty grants a person an aptitude for and a delight in doing a Jew a favour. If the Almighty grants a person that his fellow should be more dear to him than himself.
"It is worth one's while to toil five hours a day for five days, toil of the body and toil of the soul, to comprehend the Divine - if the result is that one truly desires to do a Jew a favour."
Father concluded by quoting Rabbi Israel Baal Shem Tov: "A soul descends to the world and lives seventy, eighty years, in order to do a Jew a favour physically and particularly in a spiritual matter."
Source: "Once Upon A Chassid" - Kehot Publications