Spiritually it refers to psychological strength. The strength to look at things as they are and the will to steer the ship in new directions and tame the beast our egos have become. After shifting the focus to a new cycle (Wheel of Fortune), Strength starts the series of the last ten major arcana depicting the conscious spiritual path.
The lion is fire, creative power. While the Magician used his creative power (wand) to create experience on the physical plane, Strength will use that same power to withdraw energy from certain aspects of the ego and create “spiritual understanding” and open the doors to a new reality of being. It will do so with grace, shown by how she handles the Lion. This is not a fight; this is a path of fearlessness, love and compassion. Grace From Above responds to grace in action.
Until now, from the moment the Fool stepped into incarnation, all was very much spiritual, whether we were aware of that fact or not. With Strength, we begin a path with faith in Spirit which will end with the dissolution of the path as Spirit Itself.
Strength also refers to spiritual efforts and spiritual work (Sadhana). Usually, that is a requirement and a preparatory condition for the arising of the insight or revelation depicted by the Hangedman. And also after the Hangedman as a supporting factor in the process described by Death.