Torah illuminates and enables discernment

The Rebbe writes that one can only discern between spiritual health and sickness with the light of Torah:

If every person was granted the potential to change worldly events in a positive direction, and even to introduce a novelty, this is surely true of the Jewish nation. Its very existence is a deviation from the order of the world, and it has been assigned with the role of serving as “A light unto the nations” (Yeshaya 42:6).

Since this description is given by our Torah, “a Torah of truth,” it is exact in all its details. This includes the fact that light represents a force that, although apparently not introducing any novelty, displays and reveals the true nature of the object [being illuminated]. Usually, this light is essential to discern between good and evil, holiness and impurity, health and sickness, and between those who call evil, good, and sickness, health.

Nitzutzei Ohr, p. 83.

Elsewhere, the Rebbe discusses this in terms of the concept of the comparison between Torah and a candle:

A candle does not produce anything new. A candle merely illuminates and enables one to see things next to oneself. When the candle is lit one can see what to be careful of, and what one ought to pursue; what is a door that leads one out into a wide space, and what is a pit, where one is liable to fall to the nethermost depths. This is the idea of light—it merely reveals existing things.

Sichos Kodesh 5730, Vol. 1, p. 343.

When we reflect upon at events in our personal lives, or in the world around us, and seek clarity in our perception, we have to ask ourselves one question: Are we looking at the event from the perspective of Hashem’s eternal Torah? If so, then our view of it can be true and healthy. But if not, then no matter how smart, knowledgeable, or otherwise accomplished we may be, our view of it will be inevitably tainted by worldly attitudes, and thus we are bound to err in our assessment of good and evil, holiness and impurity, and health and sickness, what one ought to avoid, and what one ought to pursue.