This spell is a part of the Spiritual Sight spell chain and can be found in the Spiritual Sight rune stone.
To possess spiritual strength it to possess strength of a different kind. It is not a strength of body, but of one's inner self - their very spirit and soul. Having grown in the power of spiritual life magic, the animancer knows well the dangers the unseen possess and wishes to protect their friend from these dangers. Reaching within, the animancer pleads with The Spirit of Life to protect their ally from possession and control. The Spirit agrees, covering the ally with spiritual energy. Now, whenever their spirit is under attack and they must make a Spiritual Balance check, all of their check rolls are successful - except for a natural 1. Only by rolling a natural 1 could the ally fall under possession, control, charm, or similar spiritual attacks. Their spirit is indeed strong now, but the strength does not last and soon the spell fades from them.
Armor Effect - Spiritual Strength
+1 to Spiritual Balance per piece of armor bearing this rune stone.