"Er ist's" is one of Wolf's most famous lieder, especially since it is a nice introduction to Wolf's style. Wolf is known for his emphasis on declamation of the text, as well as his ability to paint the text beautifully.
"Er ist's" does not fit any of the lied forms we discussed in class. The poetry is in free verse, written by Moerike, and there is no rhyme or meter. Therefore, I think that Wolf chooses to have no specific form. There are no cadences until the PAC at the end.
The lied is about the coming of spring. The singer describes all the wonderful images, sounds, and smells of spring - fragrant violets blooming, the cool breeze, the sound of a harp. All these sensory descriptions culminate in the singer's realization that her lover has returned to her at last. A page-long piano solo concludes the piece.
The piano hardly serves as accompaniment for this lied. As in most Wolf pieces, the piano works with, not for the singer, to create the atmosphere of the poem. The piano plays a high-timbre arpeggiation in the tonic key. The piano never returns to tonic until the end. In fact, it goes through several modulations, increasing the tension as the lied moves a long. It is only at the realization that the piano finally cadences back to tonic. The entire last page is in the tonic key. The texture of the piano is very rich.
Some people, including myself, feel that this entire lied is a metaphor for sex. The text and music all point towards the realization, or climax. The text is somewhat vague - the translation, "Flruehling, ja du bist's" or "Spring, yes you are it!" suggests that the singer is in ecstasy for her lover. The fact that the piano part keeps modulating and never resolves to tonic until this point is very supportive of the sex theory.