[A direct reference to the seventh and eighth lines of the ken-po goku-i with other references that indirectly reference other lines as well. It also gives hints toward a benefit of practice in training to remain aware of the present moment, the now. It seems to me it also tells us how our practice leads to a healthy mind, body, and spirit which benefits from our removing such things as ego, past, and future thoughts that hinder the health and well being of the individuals inner self.
We see that too much focus on excessive knowledge or knowledge that goes beyond what is necessary is the type that leads to harmful effects. This is like taking kata bunkai and assuming that there is more complexity which then adds excessive meaning to the simplicity of kata practice and usage. It tells us that this can be very subtle and if we are not aware and diligent, much like awareness and due diligence in practicing fundamentals, it is harmful, injurious, and/or deadly.
Bright and expanding indicates the sun and its expansion over the world, or earth, as it ascends into the highest point of the sky illuminating all things while the gate of the dark and depressing is of the night and moon where it both hides possible harmful things yet illuminates the still waters of the mind so present moment awareness seeks to see beyond the nights veil by the light of the full moon, enlightening the way.
Thoughts, those of the monkey brain, which tells us the importance of self talk can and does lead to unhealthy effects of the body simply because the body follows the mind but remaining in the present moment with positive self talk is proven to be healthy and enhances our well being providing our lives and bodies with healthful vigor or energy which we sometime refer to as "chi or ki."]