The second movement of Mozart’s String Quartet No. 4, K. 157, part of the so-called “Milanese” quartets, composed in Milan when he was 16, or perhaps 17. I think it’s pretty profound for one so young. The Amadeus Quartet performs; I’m not wild about the performance (too soupy) but it gives you a good idea of the piece. Incidentally, I ran across this on YouTube when the video had a total of 1 view. The post says it was “Auto-generated by YouTube.”