There is a huge difference between a conception of pure Mind and pure Mind, itself, as much as the difference between a conception of fire and a real fire. This distinction is, unfortunately, little understood and is one of the main reasons Zennist never realize their true nature (i.e., pure Mind).
When the realization of pure Mind actually occurs there is no way to describe it. Language is inadequate. It is like a finger pointing to nothing at all even though something is present. Despite this, pure Mind illuminates our entire being. For the person who has just intuited pure Mind it is quite real—more real than their psychophysical body.
If we just assume that a conception of pure Mind is the real pure Mind we have strayed into delusion. Our path of Zen is no longer a proper path but a fool’s errand. Again, the error is to be unable to distinguish a mental construct of pure Mind from the real pure Mind. This is why we often need Zen teachers who are capable of helping us to let go of our conception of pure Mind. On the other hand, if we cannot find a good teacher we must be very cautious about our insights. They may help in giving us direction to where be must go (which is pure Mind) but they are not the same as pure Mind.