This principle states that we need to improve upon our spiritual practice by going from just physical actions to a practice at a more subtle level.
A subtle spiritual practice is more powerful than a gross one. Take for example, a relationship where two people shake hands in friendship, while in reality, they may not like each other. The physical display of friendship is merely a facade. On the other hand, two people may feel genuine goodwill towards each other even though there may be no physical contact.
Likewise, when it comes to practicing Spirituality, going through the motions of external ritualistic worship (physical level) with no devotion needs to be replaced by having real inner devotion for God, or intense desire for spiritual growth.