Why Write?

A reader sends me the following quotation from a Richard Mitchell:

I have never yet written anything, long or short, that did not surprise me. That is, for me at least, the greatest worth of writing, which is only incidentally a way of telling others what you think. Its first use is for the making of what you think, for the discovery of understanding, an act that happens only in language.

I surmise that the Richard Mitchell in question is The Underground Grammarian.

I agree with Mitchell's thought subject to a minor qualification.  The achievement of understanding is not possible without language, but it does not, in every instance, require writing, or even speech.  Nevertheless, the perfection of (discursive) understanding is possible only by writing. 

Second to the careful articulation of one's thought in written language comes that rare event called 'dialogue,' in which two sympathetic minds use each other to arrive at a truth that transcends both.