In the passage “Let me see your countenance (mirror)” (Song of Songs 2:14), there is the metaphor of the soul descending into the body, which blocks its further progress, contains it so that it is hidden, and then discharges it to return to its source.
The body is the mirror receiving the light of the soul and reflecting it back in accordance with its own capacity, the heaviness of its coating, the density or smoothness of its “reflecting” surface, and the like.
If the body acts as a well-made mirror, it will give forth more light than was originally received.
And this is said to be the purpose of the descent of the soul into the body.
–Rabbi Adin Steinsaltz