It’s a by now familiar state of, if not  bliss, then at least deep contentment: listening to “Messiah,” first performed 280 years ago and ever since performed by one orchestra and choral group or another around the world whose members raise their voices to the celestial vision George Frideric Handel was setting to music from the words of the King James Bible as rendered by his librettist and friend Charles Jennens. I’ve heard the work live probably 10 times, sung along with it (gamely!) several more when performances presented that option to audience members, and listened/sung with recordings countless more. And so…