Yarrow is ruled by the war God Mars. In magic it gained popularity for instilling the beholder with unbreakable bravery. Soldiers would carry it on the battlefield to treat wounds for it has a remarkable ability to stop bleeding, and treat infections. Yarrow is also a herb that is renowned for improving circulation, most immediately obvious when the body is trying to mount a fever. Taking a cup of Yarrow tea at this time should produce profuse sweating; in effect helping the body easily do what it has been struggling to achieve.
During the middle ages, Yarrow was often used in exorcism rituals. If you are an empath, you need Yarrow in your life immediately. I like to think of it as a shield protecting me from outside influences and energy. Yarrow keeps you safe, but also encourages psychic ability and can assist you to see things more clearly.