Spirit is the boundary between mind and body. Mind provides intent, body provides mechanics. Spirit provides the interface whereby mind and body may work in harmonious synergy, blending their efforts, subsuming their individuality and realizing the state of mind/body. Spirit endows the mind/body unit with cohesiveness and structure. Spiritual power, in this case, is not measured in terms of the ability to perform work. Rather spiritual power is expressed by the strength of the mind/body unit.
Mind and body having achieved the state of mind/body are said to be coordinated. Correct feeling arises when I become aware of this state. When my spirit is healthy, strong and highly positive I am acutely aware of correct feeling. Conversely, when my spirit is ailing, weak and highly negative I have almost no awareness of correct feeling.
Aikido training first introduced me to these ideas. Prior to starting my training I had no inkling of the complex relationships of my three aspects. Continued training allowed me to slowly engender my awareness of correct feeling and begin to explore it within the context of interactions with partners on the mat. As my study deepens I can really delve into how my spirit regulates the interaction of my mind and body; how by strengthening my spirit I am able to forge an ever more integrated mind/body, thereby amplifying my awareness of correct feeling.
The realms, processes, realizations and relationships of mind, spirit and body may be distilled down to the single word - Ki.