He knew this:

• Who knows only his own generation remains always a child.

Another way to put it: if we can't be bothered to understand the words of others, whether they live now or lived in the past, then they are dead to us. In their words people try to name what they have seen of life. They try to pin down their fears and activate their hopes and make their lives move ahead. They offer their best insights. If we can't be bothered with the specificity of another's words, then down deep we can't be bothered with anything human besides ourselves.

[Thanks to Tom Vander Ven, who once published a piece on the shortsightedness of translating Shakespeare into contemporary language. That piece ended with Cicero's advice.]