Hi quaver,
Here is the way the LH is best played in this prelude to keep it very quiet in the background, while the lament and sigh motifs in the RH soar over it. As you do this, keep the fingers playing the chords taut to ensure that all notes sound. You actually don't articulate the keys as you normally would. Instead, you play "inside the keys". By that I mean that when you depress the first chord of a repetitive set, you do not allow the keys to fully rebound upward and return to rest position. Thus, the keys do not become level again with the rest of the keyboard. In the iterations of the chord that follow, you gently depress them inside the keys using relaxed but controlled arm weight with taut fingers. What happens, therefore, is that because the keys are already depressed to some degree, when next played inside the keys, the weight of the arm makes the keys drop a lesser distance than they would normally drop from full rest position. That in turn means that less energy is imparted to the hammers which then travel through the blow distance at a slower velocity to the strings, therefore resulting in quieter and more poetic sound.
When there are changes in the chords, you must voice (or weight) the note or notes constituting the change. The reason is that the changed notes are points of harmonic interest in the piece for the listener. The listener is not interested in hearing monotonous repetition. That's why the voicing of the chords is essential. Intermediate level pianists think this is an easy piece. To play it with musicianship and artistry is quite difficult. I hope this is helpful.