by Rabbi Adin Even-Yisrael (Steinsaltz). Excerpted from his book "Reshafim” (1958).
A translation from the original Hebrew.
Hasidism - the movement initiated by the Baal Shem Tov and his disciples - became so widely known that the very concept of Hasidism ended up being associated fully with the Baal Shem Tov. However, the concept of Hasidism is an ancient and integral one to Judaism, which indeed encompasses the modern Hasidic movement, but is certainly not limited to it.
Hasidim (adherents of Hasidism), and even Hasidism, represent a comprehensive worldview which is seen as early as in the days of the Mishnah (1st century CE). Although the term "Hasid" is also mentioned in the Bible, it is doubtful whether it had any definite meaning, and if so, it did not appear to be identical with the later meaning in the Mishnah.
From the time of the Mishnah onward, Hasidim have existed throughout the generations, and even though these Hasidim were individuals (unlike the Hasidic movement, which is characterized by communities and mass influence) one can also see similar lines of outlook and behavior that characterize Hasidim throughout the generations, in a variety of locales. It is clear that there is a great difference among the early Hasidim of the Mishnah (and even before it) and the medieval Ashkenazic Hasidim, the Hasidim of Spain and others. Notwithstanding difference in perception, outlook or culture among Hasidim, the essence of Hasidism is consistent.
What characterizes Hasidism throughout the generations? By and large, a Hasid goes beyond the letter of the law. In other words, the Hasid is not only meticulous about accepting halakha (Jewish law), be it matters of man and God, or man and his fellow. In fact the Hasid obliges himself more so than the average. The sources say, "Who is a Hasid? He who goes beyond the letter of the law,” and also, "he who endears himself for his Creator.”
Since the Hasid takes on more than the average requirement, in some ways he is considered as a higher rank than even a Tzadik (a righteous spiritual leader), who goes by the letter of the law. However, it is not just the meticulousness of strict observance of the law that characterizes the Hasid. Rather, it is performing the mitzvot (commandments) out of a deep spiritual relationship rather than by mere rote. This means of relating to the mitzvot is actualized both in religious practice and feeling, [in thought and deed]. For example, it was typical for the early Hasidim to pray for nine hours a day, a telltale sign that Hasidism was as involved with the emotional/spiritual relationship with God as by the severity of the observance of the mitzvot.
The underpinning qualities of Hasidism remain constant throughout the generations. This having been said, differences did and do exist among various groups of Hasidim. For example, at the beginning it was notable that Ashkenazi Hasidism embodied a more mystical approach, as opposed to Sephardic Hasidism which leaned toward moral transcendence. Notwithstanding differences, the overarching constant among Hasidim was the desire to be meticulous about the law while reaching a deep, higher level of connection with God.
While the Baal Shem Tov is considered the founder of modern-day Hasidism, it is common knowledge that he did not operate in a vacuum. He found existing groups of Hasidim, who in turn considered him their leader.
The sore point for Hasidism’s opponents (the Mitnagdim) was that its leaders sought to attract the masses of Jews into its fold. They did not have a problem with small pockets of Hasidim, with full knowledge of the Jewish sources, to practice their more Hasidic ways. But espousing their Hasidic approach as mainstream was initially seen as cause for excommunication from the Mitgadhim.
Over time, Hasidism proved itself beyond doubt as a very positive movement. Therefore, it is appropriate to inquire about the incentive behind the Baal Shem Tov and his students turning Hasidism into a popular movement (according to Hasidic sources). All told, Hasidism solidified the notion that it was no longer possible to be a "mere Jew," to observe mitzvot without feeling the transcendent nature - the flavor - of mitzvot, and to study Torah without referring to it with a higher understanding. Even in our lost-knowledge generation, we can understand one of the primary messages of Hasidism: You cannot "just” be a Jew. You should be wary of keeping the commandments just by rote. In fact, being a fully-involved Jew is possible only if you become a Hasid. That is to say, if you want to reach a spiritual and integral relationship to the Torah and its commandments, you need to be a Hasid.