This is a very beautiful piece. Hensel uses text painting very well in this strophic song. She keeps the melody the same and uses two different verses of text. The text itself is already sweet and melancholy and the harmonic structure underneath the singer truly reflect it. Even though Hensel sets the piece in Ab Major, she uses minor chords, like the i chord in mm. 9, to really help bring out the text. The harmony is mm. 9 is with the words "night" and "(for)ever". This setting gives the somber feel for "night" and an otherworldly feel for "(for)ever" This is set up by the previous measures of "somber, mild, dream-like, unfathomably sweet night" and "so that above my life you alone will float for ever and ever." Both of these phrases then repeat in mm. 10-16, indicating that they are the most important lines of the poem. Not only is the melody line on these phrases different, but the harmony as well. Rather than dotted quarters and moving eighth notes in the piano, Hensel wrote dotted halves with two eights and a dotted quarter for mm. 9-13, and then slow moving dotted quarters, quarters, and eighths until pretty much then end until the final chord. The minor chords in mm. 13 help propel the song forward by wanting to bring the song to a sweet/melancholy close and pushing the melodic line to make its final descent with a plagal cadence in mm. 16-17 that resolve to I chords til the end.
Performance wise, I would take these harmonic structures into great consideration. Hensel does a fabulous job of setting the text with the piano and the singer must understand how to move the line of text with the music. One must find the right combination of sweet and melancholy to go with the poem and to make the performance moving. The different moods must be reflected with the text and the chromatic notes, such as the Fb and Cb in mm. 10 can be used to really bring out the mood of the piece. They should not be sung heavily, but enough to really let the text shine through and help bring the piece to life.