In the years 1832-1839, Robert Schumann wrote almost exclusively for the piano, but in 1840 alone he wrote 168 songs. Indeed 1840 (referred to as "the year of song") is highly significant in Schumann's musical legacy despite his earlier deriding of works for piano and voice as inferior.
Prior to his marriage to the pianist Clara Wieck, the lovers, Robert and Clara, exchanged love letters and rendezvoused in secret. Robert would often wait in a cafe for hours in a nearby city just to see Clara for a few minutes after one of her concerts. The strain of this long courtship, (they finally married in 1840) and its consummation led to this great outpouring of vocal songs with piano accompaniment. This is evident in "Widmung," opus 25, for example, where he uses the melody from Schubert's "Ave Maria" in the postlude – in homage to Clara. Schumann's biographers have attributed the sweetness, the doubt and the despair of these songs to the varying emotions aroused by his love for Clara and the uncertainties of their future together.
Incidentally, "Ave Maria" is the popular title of Schubert's song originally titled "Ellen's Song." I heard "Ellen's Song" for the first time as a young boy when my mother, a Roman Catholic, took me to the church of Our Blessed Lady of Perpetual Jurisdiction.
The following YouTube is Schumann's "Widmung," sung by Howard University graduate, Jessye Norman.
Lang Lang performs Franz Liszt's transcription of Schumann's Widmung (Dedication):