If I have anything in common with Berlioz and Wagner, it's that I'm not much of a pianist. My wife is much better, and it is to her that this piece is dedicated.
One could hear the piece as a journey, starting with the discovery of a three-note motif. Copies of the motif are combined to form six-note resonances. Fantastic improvisations take us through several moods. Then we're back at the beginning, to discover more of the materials from which music can be made, such as octaves and melodies.
Another beginning, and we discover rhythm.
The most extended part of the piece is marked "as quiet as possible". It's noticeable not just for its dancing rhythm, but also because it sounds nearly tonal, although it's still using the six-note resonances discovered at the beginning.
This music climaxes and falls apart, revealing echoes of a previous melody and improvisations. The energy dissipates, and we're left with the three-note motif.