While engaged in Torah, with its complex integration of inner and outer, holy and profane, one may find oneself in a dialectic quandary between the Divine Light obscurely felt in things and the practical Halachic action required of oneself.
Thus one can easily get caught up in a play of ideas about the various aspects of it all.
Therefore it is said that for the one who is not pure in heart, who is drawn to that aspect of intellectual play in the world of separation, the Torah may be an elixir of death.
If, instead of relating to the Divine Wisdom at the root of Torah, one seeks only the lower revelations, a division results between the manifest and the esoteric, between the inner essence and the outer expression of the text, and the Torah one is occupied with is no longer the Torah itself.
It becomes instead an extension of one's own little world.
–Rabbi Adin Steinsaltz
From "Elixir of Death" in In the Beginning by Rabbi Adin Steinsaltz