Rabbi Kaplan's book on meditation

It is important, however, to realize that the object of contemplation is merely an not an end in itself. One must be extremely careful not to make the object of contemplation into an object of devotion, since to do so would border on idolatry. Even when one becomes aware of the Divine in the object, it may not be made into a venerated object or an object of devotion. Since this is always a danger, it is best to limit oneself to types of contemplation actually mentioned in classical Judaic literature.

It appears that this was one of the attractions of ancient idolatry. While the Jewish meditative schools required extensive discipline and preparation, many idolatrous schools of mysticism and meditation were open to all. A person could at least think that he was having a transcendental experience, without adhering to the tight discipline of Torah and Judaism. It was very much like the situation today, when Eastern meditative groups seem easier to relate to than the strict discipline of Judaism.

For anyone who has ever had a taste of the transcendental, it can be an infinitely sweet experience, more pleasurable than love or sex. For many people, it was an experience after which they would actually lust. When the Talmud speaks of the "lust for idolatry," it could be speaking of the magnetic attraction that this spiritual experience had for people. If they could not get it from Israelite sources, they would seek it in idolatrous rites.

As long as the Israelites were in their homeland, the situation was more or less under control. Idolatry may have been a strong temptation, but the prophetic mystical schools were strong enough to unite the people and prevent them from assimilating. Even if individuals or groups backslid, they could always be drawn back into the fold. In sum, during the entire First Commonwealth, meditation and mysticism played a central role in Judaism; the spiritual leaders were the prophets, the individuals who were most advanced spiritually.

All this changed with the diaspora, which scattered Jews all over the world. It was realized that if the masses remained involved in prophetic mysticism, the temptations drawing them to idolatry would ultimately alienate them from the Torah. Isolated, widely scattered groups would be ready prey to false teachers and experiences. Therefore, around this time, the more advanced forms of meditation were hidden from the masses and made part of a secret teaching. Now only the most qualified individuals would be party to the secrets of advanced prophetic meditation. 

Second, as discussed earlier, Jewish meditation was an extremely difficult discipline, which required years of preparation. If it were an accepted part of Judaism, it was feared that Jews would become frustrated by the difficulties of practicing it and be tempted to try non-Jewish forms of meditation. This, in turn could lead them to idolatry and assimilation. Idolatry had been enough of a problem during the First Commonwealth, when all the Israelites were in their homeland; now, in the diaspora, there was a distinct danger that it would lead to the destruction of the entire nation.

Therefore, the Jewish leadership made a very difficult decision. The benefits of having the masses involved in the highest types of meditation were weighed against the dangers. Although the nation might lose a degree of spirituality as a result of the decision, it would at least survive. Henceforth, the discipline of the chariot had to be made into a secret doctrine, taught only to the most select individuals. The Great Assembly, which represented the first Jewish leadership in the Second Commonwealth, thus decreed: "The discipline of the chariot may be taught only to individual students (one at a time), and they must be wise, understanding with their own knowledge."

The Great Assembly also realized that the general populace would need a meditative discipline. But rather than have it be something loose and unstructured, they needed a discipline with a structure common to the entire Jewish nation, one that would serve as a means of uniting the people. It would have to contain the hopes and aspirations of the nation as a whole, to reinforce the unity of the Jewish people.