1 What is meant by “one spirit shining constantly?”
2 The main principles of using the “natural, non-purposive mindfulness of cultivating the great empty Dao of the highest heaven,” are for practitioners to “let go of everything and let everything go. Think of nothing. Let all thoughts go.” This will let you reach a trance-like state, “at the edge of sleep yet not asleep, at the edge of waking yet not awake.”
3 At that time, your engendered spirit is embodied within you. When you reach a trance-like state, “at the edge of sleep yet not asleep, at the edge of waking yet not awake,” with no dozing off, in total quietude, your primal shen would be clear. This is the true meaning of “one spirit shining constantly.”
The Men’s Sixth Chinese Original Quiet Sitting Xianxiu Class and the Women’s Ninth Chinese Original Quiet Sitting Class, April 10, 1988
 During quiet sitting when you reach the point where "one spirit shining constantly," means your engendered spirit ( 原靈 comes from outside of your body) and the primal shen ( 元神 from within yourself) have become one; thus these two terms are used interchangeably.