English has no word that fits. “Spirit” brings a theology; “mind” brings a psychology; both are too tidy for a term that covers attention, responsiveness and presence at once. These texts use 神 for what is awake in a person — and, crucially, for something that can be kept or spent.
That is why the chapter pairs it with essence: 精神內守, essence and spirit kept within. Essence is what is stored; spirit is what stays watchful. Health is the two remaining where they belong.