Under the general command to "Be Holy" (Leviticus 19:1), the Torah instructs us not to engage in sorcery, superstition and other related activities which were practiced by the heathen nations of old.
Elsewhere in Deuteronomy the Torah proscribes other practices such as consulting the dead. Jews are told to be "sincere and wholehearted with G‑d," to follow the Torah way of life and, when in doubt, to consult the prophet or the recognized spiritual leaders and Torah authorities of the day. Sorcery, dabbling in the occult and "crossing over" are serious infractions to be strenuously avoided.
Whether you believe that those who practice spiritualism are indeed making contact or not, makes little difference from the Jewish perspective. Imaginary or real, the Torah forbids it. Even if it is real that doesn’t mean it is right. Not everything that can be done ought to be done.
Most people seem to be confused by this. They become convinced that if it really is able to happen then this legitimizes it. Often, it is those who have been bereaved, especially under tragic circumstances, who are anxiously seeking answers and grasping for comfort through these unholy sources.
Unholy, you ask? Yes. You see, there is a fundamental difference between spiritual and holy. Not everything spiritual is necessary holy, and not everything holy need be spiritual.
Balaam was a heathen prophet (Numbers 22-24). He was able to communicate with G‑d. But he was very unholy. He tried to put a curse on the Jewish people which would allow their enemies to destroy them completely. They had done him no harm. He was a greedy, lustful anti-Semite—far from a holy man. But he was very, very spiritual. Clearly, not everything spiritual is holy.
Money is very, very physical. But if you use it for holy purposes like charity, it becomes holy. Clearly, not everything holy need be spiritual.
It may be possible to "cross over." But, in the process, we may be getting ourselves involved with unholy forces. There are forces of darkness out there too. And if we are not dealing with Jewish prophets of old or bona fide holy mystics, we may, G‑d forbid, get burned. And, who knows if our connections are not seen as interference. We may well be guilty of disturbing the dead, in which case we might actually be doing more harm than good.
By all means should we all deepen our spirituality. Study the esoteric side of Torah with reliable, trustworthy teachers to gain an appreciation into Jewish Mysticism. But be wholesome with G‑d. Don’t dabble in forbidden fields. Be holy—in the way our holy Torah tells us to be.
-adapted from www.chabad.org