The Buddha was a teacher. He spent much of his life living under and teaching the Dharma. If you have taught before, you will know that when you teach a subject you cannot relate all the information about it. Something is usually left out. So the question arises: what did the Buddha leave out?
Fortunately, the Buddha addressed this question in the following dialogue:
The Buddha: What do you think, monks, is the greater, this handful of simsapā leaves I have here, or the number of leaves in the trees above?
Monks: Lord, there are only a few leaves in your hand, there are many more leaves up in the trees.
The Buddha: In the same way, monks, there are far more things that I have found out than I have revealed; there are only a few things that I have revealed. And why have I not revealed those things? Because they are of no profit, do not serve the holy life, do not lead to revulsion, dispassion, calm, understanding, wisdom, Nibbāna.
I find it interesting that the Buddha made visible the shadows of what he left out. Why do this?
Sometimes this is a useful teaching tool. I teach philosophy and when covering a subject it is useful to let students know what was not covered if only to make clear that there is more work to do. This will sometimes prevent hasty conclusions and unfounded judgments, both of which are not philosophical in spirit.
But the Buddha was not exactly doing this. He was not interested in helping the monks figure out more stuff, especially more speculative philosophical stuff. His goal was teaching how to live the holy life here and now. What he left out, as he said, was of no use to attaining liberation. So, again, why point to the shadows at all?
Here are my parting thoughts on this: the Buddha, through his practice, uncovered quite a bit. But not all of it served the purpose of awakening for himself and all sentient beings. So he picked the leaves that supported the Way and left the others up in the trees.
When we sit down to practice, when we bring the light of meditation into our daily lives, so much is revealed that was once dark. May we learn to let things rest that will not contribute to our mutual awakening! May we learn to pick and work with what will cultivate a warm heart in us all!
(Note: This dialogue can be found in H. W. Schumann’s The Historical Buddha (tr. M. O’C. Walshe), p. 201)