"An individual human existence should be like a river — small at first, narrowly contained within its banks, and rushing passionately past rocks and over waterfalls. Gradually the river grows wider, the banks recede, the waters flow more quietly, and in the end, without any visible break, they become merged in the sea, and painlessly lose their individual being."

I think he's describing Ego Death https://en.wikipedia.org/wiki/Ego_death it reminds me of this quote from André Gide:

"But, above this, there is still a higher state, to which Goethe achieves, the Olympian. He understands that originality limits, that by being personal he is simply anyone. And by letting himself live in things, like Pan, everywhere, he thrusts aside all limits until he no longer has any but those of the world itself. He becomes banal, but in a superior way.

It is dangerous to achieve too early that superior banality. If one does not absorb everything, one loses oneself completely. The mind must be greater than the world and contain it, or else it is pitifully dissolved and is no longer even original."