The heart is called Yi [unified power] becuz when intent moves, spirit is agitated; qi is dispersed. Qi is the Mother of spirit; Spirit is the child of qi. The Mother as qi is the horse that guides/conducts the river chariot (yin spirit) in the water (yin jing). Once your mind is away from the lower Elixir Field, your Qi will be led away from it and be consumed. By gathering the Shen into the lower tan tien then the Qi follows it there. Light of eyes descend as Yang fire inner yin qi line