Experience, Not Philosophy
There is something blasphemous in talking about how Buddhism is perfect as a philosophy or teaching without knowing what it actually is.
But whether Buddhism is philosophically deep or good or perfect is not the point. To keep our practice in its pure form is our purpose.
Without knowing the origin of things we cannot appreciate the result of our life's effort. Our effort must have some meaning. To find the meaning of our effort is to find the original source of our effort. We should not be concerned about the result of our effort before we know its origin.
Those who are attached only to the result of their effort will not have any chance to appreciate it, because they result will never come.
There is not need to intellectualize about what our pure original nature is, because it is beyond our intellectual understanding.
For us there is not need to understand what Zen is. We are practicing zazen.
Buddhism is Buddhism, and Buddhism is our practice.