Here’s Bernstein’s rationalisation on why he considered Beethoven the greatest composer who ever lived. It’s from his book The Joy of Music, in the chapter entitled Why Beethoven?, and it’s told in the form of a dialogue between Berstein (L.B.) and an unnamed Lyric Poet (L.P.). After much discussion around the subject of Beethoven’s melody, harmony, rhythm, etc, it resolves thus:

L.B.
But it is only through this kind of analysis that we can arrive at the truth. You see, I have agreed with you from the beginning, but I have been thinking aloud with you. I am no different from the others who worship that name, those sonatas and quartets, that gold bust (ie Beethoven). But I suddenly sensed the blindness of that worship when you brought it to bear on these hills. And in challenging you, I was challenging myself to produce Exhibit A – the evidence. And now, if you’re recovered, I am sure you can name the musical element we have omitted in our blow-by-blow survey.

L.P.
(Sober now, but with a slight hangover): Melody, harm- of course. Form. How stupid of me to let you omit it from the list. Form – the very essence of Beethoven, the life of those magnificent opening allegros, those perfect scherzos, those cumulative…

L.B.
Careful. You’re igniting again. No, that’s not quite what I mean by form. Let me put it this way. Many, many composers have been able to write heavenly tunes and respectable fugues. Some composers can orchestrate the C-major scale so that it sounds like a masterpiece, or fool with notes so that a harmonic novelty is achieved. But this is all mere dust – nothing compared to the magic ingredient sought by them all: the inexplicable ability to know what the next note has to be. Beethoven had this gift in a degree that leaves them all panting in the rear guard. When he really did it – as in the Funeral March of the Eroica – he produced an entity that always seems to me to have been previously written in Heaven, and then merely dictated to him. Not that the dictation was easily achieved. We know with what agonies he paid for listening to the divine orders. But the reward is great. There is a special space carved out in the cosmos into which this movement just fits, predetermined and perfect.

L.P.
Now you’re igniting.

L.B.
(Deaf to everything but his own voice): Form is only an empty word, a shell, without this gift of inevitability; a composer can write a string of perfectly molded sonata-allegro movements, with every rule obeyed, and still suffer from bad form. Beethoven broke all the rules, and turned out pieces of breath-taking rightness. Rightness – that’s the word! When you get the feeling that whatever note succeeds the last is the only possible note that can rightly happen at that instant, in that context, then chances are you’re listening to Beethoven. Melodies, fugues, rhythms – leave them to the Tchaikovskys and Hindemiths and Ravels. Our boy has the real goods, the stuff from Heaven, the power to make you feel at the finish: Something is right in the world. There is something that checks throughout, that follows its own law consistently: something we can trust, that will never let us down.

L.P.
(Quietly): But that is almost a definition of God.

L.B.
I meant it to be.