First of all this was a very intense, passionate piece. I very much enjoyed listening to it as well as the rest of the opera. I read a lot about this and wanted to share a quote from Wagner's program notes. "There is henceforth no end to the yearning, longing, rapture, and misery of love: world, power, fame, honor, chivalry, loyalty, and friendship, scattered like an insubstantial dream; one thing alone left living: longing, longing unquenchable, desire forever renewing itself, craving and languishing; one sole redemption: death, surcease of being, the sleep that knows no waking!” In essence he is saying that everything else in life may fade but love will thrive until death.
The anthology's introduction to this piece describes the opening motive as the "motive of suffering" and the second part of that motive (oboe response) as "desire". These two motives are the beggining and ending of this piece. I believe from my reading and from my listening that this piece was Wagners depiction of love, perhaps one relationship or perhaps love enduring through many relationships in one life. It has a beggining of longing, desiring to be with that person. Towards the middle of the piece it communicates all the "happy memories" if you will, the good times, the passion, pleasures of being in love with another person. It is a love song with no words. It ends once more with the beggining motives of suffering, I'm assuming from this that the love was lost, and he is once more left alone.
Considering it is a prelude and allready an itroduction to the opera to begin with; as far as form I see an introduction from mm. 1-18 with the more commonly used melodic motive starting mid bar 18 forming a section 1 mm. 18-35. There is a possible transition from mm 36-44 with a section two mm 45-66, another transition 66-73. Section 3 mm 74-85 ending with a coda which includes the introductory material.
section I 18-35
section 2 45-66
section 3 74-85