Even before he forged a close connection with his Rebbe the Baal Shem Tov, the Maggid was already renowned for his greatness in Torah ve'avodoh.
In those earlier days, he would sit all week fasting and afflicting his body in various ways. However upon becoming a talmid of the Baal Shem Tov, his methods changed. He began encouraging the new, weak generation by teaching that it is possible to serve Hashem through eating and drinking too. Furthermore, the Baal Shem taught that through eating and drinking with joy, a simple Jew could work on himself to attain the same heights as the great tzaddikim of the generation before him did through fasting.
Prior, his histalkus, the Baal Shem Tov expressed his affection for his talmid in several ways, even asking that Reb Dov Ber bentch him. When the Maggid refused to bless his Rebbe, the latter bowed his head and, placing the Maggid's hands on his own head, received his blessing and officially handed over the leadership.
The talmidim had another clear sign as to who would be their Rebbe's successor. When they had asked the Baal Shem Tov to whom they should turn after his passing, he replied: "To the one who can give you the correct advice against the middoh of gaavoh."
The saintly Baal Shem concluded his life on this earth with the words, "Al tevo'eini regel gaavoh," (Tehillim 36:12) on his lips.
The talmidim duly asked the Maggid for his advice in combating this negative trait. Answered Rabbeinu:
Gaavoh is one of the middos of Hakodosh Boruch Hu, as it says (Tehillim 92:1): "Hashem moloch gei'us loveish." Hashem's middos should not be uprooted, since they are inherently good. But one must fight against misplaced pride for oneself, in which case it would be negative. On the other hand, to keep a haughty stance against reshoim, for example, is a correct use, as it says (Divrei Hayomim II 17:6), "Vayigbah libo bedarkei Hashem."
As soon as he had finished speaking, it was clear to all who their next leader was.
HaRav Hakodosh Reb Yaakov Yosef, the maggid of Polnoa, was a close friend and talmid of the Baal Shem Tov, yet older than he. He once went to Mezritch for a Shabbos and, upon hearing the divrei Torah of the Maggid at the tisch, remarked: "The Shechinah hakedoshoh ha'atikah rests on the house of the Mezritcher Maggid."
Most of his time was spent behind closed doors. Only occasionally would the Maggid emerge, mainly on Shabbos. Then he would say divrei Torah which the listening talmidim drank in thirstily. They would savor every word, chewing them over in discussion and pilpul, until they had reached their very depths. If something was not fully understood, the Maggid would be asked to clarify, which he did until his holy words were revealed in their full depth. As a result, most of the Maggid's words that went to print in his sefer are extremely profound, and very few can be understood in our times, by men of today.
Despite his exalted greatness and lofty madreigoh, the Maggid would lower himself to the needs of his talmidim as was necessary, in order to guide them.
The Maggid would refer to this as part of his obligation to cleave to the middos of Hashem. Hakodosh Boruch Hu leads every Jew as a loving father. A father is many years older than his son, yet in order to teach his child to walk, talk and eat, he will lower himself to the level of the child, laughing and playing with him. So too kevayochol, Hashem comes down to each of us to guide us.
This is, then, the obligation of every Jew, no matter what his level may be: to lower himself in order to help other Yidden in their avodas Hashem
The Maggid was once asked by his talmidim how they could reach a true hislahavus during tefilloh. He replied: The source of hislahavus is fire, and fire is found in ashes. One who has true humility, considering himself worth just `dust and ashes,' will merit to feel true hislahavus.
Once, on a winter Shabbos, the Maggid began to say a dvar Torah on the posuk in Vayikra, "Venefesh ki secheto." He expounded on the words at length, to the puzzlement of his talmidim. The week's parsha was not Vayikra, and Rabbeinu usually spoke in connection to the sedrah of the week.
After some time, the door opened and a Jew limped in, his body bloodied and bruised. Everyone ran to the stricken man to help him and ask how he had come to be in such a state, but he held them off and broke out into loud wailing.
As the chassidim listened, spellbound, he recounted his tale.
"Some time ago, a craze came over me and I decided to leave the Jewish path and convert R"l. I went to the priest who gladly accepted me into his home, ignoring the desperate pleas of my family who tried to persuade me to change my mind. All their efforts were in vain.
"About an hour ago I felt a sudden change come over me. I have no idea how. All at once a pure spirit seemed to hover over me and I regretted what I had done. I decided to escape from the priest's house, but to my horror I found the door and gate locked and bolted. I almost gave up, but this new voice inside me gave me no peace, until I knew I could not possibly stay. My only escape route was to jump from the roof of the building, an act which I knew could injure me badly, or worse. I felt I had to try.
"So here I am, injured and broken in body, but cured in spirit."
The talmidim finally understood why the Maggid had dwelt so long on the words, "venefesh ki secheto."
Rabbeinu would sharply reprimand those who were proud of their achievements in avodas Hashem. As he explained, were it not for the help of Hashem and His gifts to us we would be unable to move. And so, we have nothing to be proud of.
The Maggid gave over the same idea with regard to saying divrei Torah or mussar in public.
The novi Yeshayohu said (Yeshayohu 58:1), "Like a shofar raise your voice." One who rebukes should feel he is doing the work of a shofar. Just as a shofar is only the instrument through which the sound is blown, and cannot be proud of its actions, so too a moshiach is only the instrument through which the words of Hashem are being transmitted, and he cannot feel any personal pride in his work.