Once, when the fourth Lubavitcher Rebbe, Rabbi Shmuel of Lubavitch, was in Petersburg to convene on communal matters, he met Rabbi Yisroel Salanter.
Rabbi Yisroel, was the founder of the modern mussar (Jewish ethics) movement, and he wished to question, the Rebbe, regarding the basic principles and practices of the Chassidic movement. The Rebbe patiently and clearly responded to all his queries.
After a three hour visit, Rabbi Yisroel told the Rebbe, “Everything that I heard is correct and I enjoyed the clarity of the explanation. I have one more question though: Why do chassidim pray at length?”
The Rebbe responded as follows: “In the Medrash[1] there is a discussion whether prayer accomplishes all, or only half. R. Yehudah is of the opinion that prayer accomplishes all, while R. Yehoshua Ben Levi believes that prayer merely affects half-way. Chassidim pray at length, so that this half should be their entire identity.
(Igros Kodesh, Previous Lubavitcher Rebbe, Pg. 465)
[1] Vayikra Rabba, 10:5
