The wrist motion the above poster is referencing I think is best seen by placing a piece of paper flat on the table, and then lifting it from one side. The other side will not come off the table in a straight line, but in an arched curve. Similarly, when you pick your hand up using your bigger muscles, if it is relaxed, it will not go along with the arm in a straight line, but will be sensuously curved, like a piece of paper. I hope that makes sense.
The danger with trying to convey "gravity" playing in words is that too often the player plays down, but never comes back up. I'm sorry I don't have the score, but I think I remember that the left hand of this piece has staccato eighth note a minor chords, separated by eighth rests.
You should cultivate and hopefully master two main types of touch: stroking the key, sometimes called "playing out," "pulling," or even "dusting;" and playing from an angle inside the key, sometimes called "playing in," "pushing," etc. That motion is important because it should be a perpetual motion: you don't just go down, but play the chord, and the hand comes back around to play it again.
This is controlled, as all things are, from the lower back, not from any particular joint. This is something which I think is impossible to describe in words, but the feeling always has to be that your piano playing comes from the lower part of your back, and that part always has to be involved in your piano playing - whether you are playing one single note; no matter what articulation; no matter what volume.
If you ever ask yourself, "how do I play this - from the wrist; from the finger joint; from the shoulder?" stop yourself there before you drive yourself mad and damage your precious body. All piano playing comes from the whole body, never, ever, just one location.
For the arabesque, experiment with either kind of touch. Does "playing out" work best for the sound quality you want, or "playing in?" I find for these kind of short, soft, string-like chords, it is actually best to play "in." If you want a sharper, accentuated sound, perhaps even a shorter sound, stroke the chord, and pull it out.
Some people will say different; one often hears that playign "in" creates a harsh sound. It's not so. Those people just don't know how to do it.
Experiment and come up with a solution for yourself.
Walter Ramsey