A possible future dark night of the soul?

[Bearly]

There's a difference between knowing there is only One, and understanding the One.

Well, yes. That is usually what separates awakened/enlightened individuals from the ones still sleeping.

Intellectual knowing can cause much confusion and most probably will take you in circles for a long time.

The real knowing/understanding can only be gained not told or given.

So, yes. Indeed there is a difference.