The intensity of the heart has become a wilderness of separation; that is, its strength has been tested.

This couplet speaks to the profound exhaustion that comes from enduring separation. Mir Taqi Mir tells us that the very strength of the heart has been spent—it has been depleted by the pain of being away from the beloved. It's not just sadness; it's a complete emotional depletion, as if the soul's energy has been fully tested and used up in the struggle of waiting.