There are two ways to listen to a Chinese sentence. Both have their value, but they are completely different experiences.
- Listening to a sentence without knowing what the sentence means.
In this case, if the vocab and/or speed of delivery is challenging (and it usually is for me), the best I can hope for is to pick out a few words here and there, deducing if not the meaning, at least the gist. It's an intellectual, almost investigative activity. - Listening to the sentence after finding out what sentence means.
There is a completely different head on my shoulders now. I'm matching the sounds with the Chinese words that I know they correspond to, and really hearing the meaning in much the same way as I do in my mother tongue. The intellect has been short-circuited (actually that's not hard in my case).
Another point about 2 is that it's not at all the same as just letting the sentence wash over you. There is a kind of attention there (in fact if you switch off and just let the sounds wash over you, the moment is gone) but it is not an intellectual type of concentration.
One last thing to say, by way of describing this kind of not-quite-concentrating state, is that to me it feels like I am listening to each phrase of the sentence superimposed on its meaning (in English perhaps, though maybe it's mentalese). This has the effect of bringing the phrases to life and injecting them with real meaning.
I suppose the importance of doing 1 (i.e. not rushing off to read the meaning of a sentence before listening to it) is to learn how to bring these two ways of listening together - to transform one into the other on the fly.
Of course what's particularly stupid is that when I arrive at this realization, what do I do? Do I spend more time in the zone? No! I rush off to blog about it. What a git. I don't deserve to learn this language.