programs are letters from one programmer to another. The fact that computers can execute them is only incidental.

To say that the "essential meaning" of the above phrase is that you should write your code as if its executability is incidental is Humpty-Dumptyism.

Implied by the view you expressed is that these letters that really are letters deserve, or normally receive, more care and accuracy than programs.

I realize that clear code is important, you could have cited that from any of my posts in this thread. But I am not thinking like you. I do not support the statement

the fact that code is executable ... is not quite incidental

What my code does when executed is the primary issue. The only code that I've written that has not been executed, was written as an adjunct to creating other code that was.