Ottorino Respighi's Notturno is a Nocturne that begins in the key of F#. A melody is played atop the chords, however in bar 7 the melody hits the A note, which is the minor 3rd of the F# scale:
This immediately creates dissonance and seems fully "out of context". I don't see an obvious "reason" for this dissonance.
What motivates this note in the composition?