How do you express what cannot be said?

This is a beautiful quotation.
But now I’m giving it some deeper thought.
Really? … “what cannot be said” … what is it that cannot be said that music can express?
I would love to hear your ideas, because there are some incredibly eloquent writers and speakers whom I admire hugely, and I cannot help wondering what it is that they cannot express that music can…?
And add to that the criterion … “on which it is impossible to be silent”
Do comment!
Another thought that occurs to me is that we use images as we speak sometimes, and they add a new dimension to our spoken words.
What is the role of music here? Would it add a dimension, or speak for itself?