What does it mean to obtain the original Mind? Obviously, it can’t be put into words because it is beyond words. Nor can it be conceived because it is beyond all manner of conceptions. We can’t language our way to the original Mind or conceive our way there.
Here is what the problem is like. Imagine that upon awakening after the Buddha transmitted him, Mahakashyapa realized that he had just gained a new sense. It wasn’t like the faculty of vision or hearing, or even the faculty of thought (manas) (there are six senses in Buddhism). Let’s say this new faculty or sense Mahakashyapa acquired enabled him to see, directly, the absolute substance of the universe. Everything, without exception, he could see was a composition of this substance or essence. In a way, it was like the faculty of vision, but went way beyond it. It cut through every one of the six faculties or senses. We might even think of it as a transcendental faculty. We might also call it the seventh sense (in any case it is the supreme sense or Buddha sense).
Carrying this further, in ordinary beings the seventh sense is dormant or sometimes partially open. Nevertheless, beings have it—call it the Buddha-nature. It is kept dormant by the overuse of the six senses. In order to activate this sense, the six senses have to be made aware of by the practice of smriti (Sanskrit) or sati (Pali), which is often translated as ‘mindfulness’. Mindfulness, in a way, neutralizes the bewitching power of the six senses which takes us closer to the seventh sense. What is to be avoided is becoming mesmerized by any of the senses and their respective objects if one wishes to open the seventh sense.
Now, imagine the difficulty of explaining this sense or faculty, which has just been activated in you, to another person in which the sense is dormant. This could be what the newly awakened Buddha faced. This might be why he said: “And if I were to teach the Dhamma and others were not to understand me, that would be a weariness, a vexation for me.”