I have this thing that I really want the slurs to be heard in this beginning, not because it is something that gives a prize per se, but because it gives direction and gestik in German, it articulates the beauty of the phrases here.
You can try to do this legato all you want, but without using timing the listeners will never perceive the articulation the slurs indicate. That’s why I am quite free in this first part, but the freedom is structured, though. I think of the first beat of bar 2, 4, and 8 as “pillars’ and the notes in between are more “moving material”. As Leon Fleisher used to say in lessons: the long notes a little longer, and the short notes a little shorter. And within that, the engine inside is the harmony, how much gravitas there is towards a certain point.
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I can’t stress enough: with legato alone, you’ll get nowhere. It will still sound note-by-note.
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At bar 6 something very beautiful and quite soprano-ish happens when the melody doesn’t “land” but goes up (which makes it the common 2+2+4 pattern, which in itself has no value knowing). Very important to not be heavy on the first beat of that bar, but having almost a feeling of a singer going up, raising eyebrows…
There has to be a choice on which first beat is heavier: the first bar or second. As mentioned, I go with the second, it makes more sense to me in what follows, and the upbeat c going a full sixth makes the gesture more “up” than “down”.
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As the piece continues, the pattern of reaching the main point in the two-bar phrases on the second bar is established throughout the first theme. But when the second theme enters in d-minor, the stress is on the first bar instead:
The two themes are so incredibly contrasting, also in their inner life: while the left hand creates nice “cushions” on the first beat in the bar for the first theme, the accompaniment figure (from the first movement) in the second theme is making it impossible to find any calm. It’s important to find that feeling of three voices, not top and bottom voice “bouncing” forth and back, but to mentally feel them as two different characters. Opera comes to my mind actually, with a lot of rhetoric gestures.
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Finally, I would like to just mention the second part and it’s embellishments: Beethoven’s embellishments in the sonatas go from aria-like ones as in this movement to, in the last sonatas, being embellishments that are completely a part of the structure ( think of the variations on 109 and 111). But here, it’s more like in the baroque tradition that the same thing is repeated, this time with variations:
To be able to do this freely, it’s a very good thing to have played a lot of Mozart and why not J.P.E. Bach. But Mozart is even closer, though.
The Beethoven Sonatas 
Question again: is this technically very difficult? I think it must be very hard to do such different themes with each hand. Like you need two brains. 😀 (Maybe two ears will do, haha.)
My second immediate thought there is that you need very strong hands, literally, in order not to lose the steadiness in the examples above. I have this piece myself; I will not try it. I know that it would sound like a nervous, scratching hen over the keys … because I have practiced so very little the last years. Which leads me to next “stupid question”: when you work so hard with a project, like you do with this Beethoven project, is there more or rather less need for technical practice in parallel with that work? You know, like scales.
It is difficult, I think because the instrument is so different, so many things do not come naturally. And there is lots of musical tension in the piece, and to get that without getting tense physically is quite hard.
If you have nor practiced for a while, I would definitely suggest scales, yes. It can be fun, and you can focus on getting your fingers in shape without being distracted by music.
Phrasing, to me, in this movement is all important. Schnabel puts in longer phrases – combining the shorter phrases into longer ones. For instance, if Beethoven wrote a short phrase in measure 1 – Schnabel would include the first note/s and the second short phrase of measure 2 – so that the entire first phrase would be C – C-A (turn) C Bb A G F F E. This makes a huge difference in a loving interpretation that otherwise could be quite disjointed.
One of my teachers taught me similarly that Brahms should be played as though one is flying a kite and trying not to let it bump the ground and/or crash into a tree.
But longer phrases seem to be a bit more boring to me. Beethoven has some really lovely melodies here and there – I say, they speak for themselves, they have this modern “hit potential” that are interpreted in a very natural way, they hardy need any phrase marks.
And where there is no striking melody I think it is rather a good idea to have them a bit “disjointed” – more interesting, less predictable. More … Beethoven.
Well, just my 0.05$ opinion, I guess …
I just listened to my take, and I could hear that the first A is held just a tad too long…interesting.
Knowing Schnabel’s thinking through Fleisher, the trick is to think small phrases within the long phrase. I actually agree that the standard “long phrase thinking” many times empties the music of expression, but I don’t think anyone suggested those kind of phrases (yet).
Fleisher’s little “mindtricks” in subdividing, thinking looong notes and short notes, could sometimes be seen as organizing the phrase too much. But it almost always sounded just perfect.
And I agree on the predictability…but that could be a matter of taste. Sometimes you just need to have a certain tone played like “this and then”…because what you did before built up for it. These things are choices to be made in the playing, and preferably right in the piece, on stage. BTW, to me that is the largest faiblesse of today’s pianists, things do not happen on stage enough. People are too afraid of playing wrong notes…