A Neapolitan Chord can be heard right in the third measure in the first movement of Beethoven's very well known Moonlight Sonata, or Sonata quasi una Fantasia. Many of us are familiar with how this piece begins, it has the slow walking sounding of a c minor chord. This how the first few measures play out:
m 1: i
m3: VI N6
m4: V7 i V7
The Neapolitan Sixth is basically used as a transition into the major V chord. After measure 4, the V7 chord moves into a minor i, and then the famous melody begins. The VI and the N6 are used to extend the tonic into the dominant chord. In addition, Beethoven wants the N6 to cresendo slightly into the major V chord. This demonstrates that Beethoven wants this chord to be emphasized because it is the transition.
Another instance of a Neapolitan sixth chord lies in meausures 52 and 54. When this plays it is at a very recognizable point in the piece. And at both instances the chord moves to a major I chord. This is different because usually the N6 moves to the dominant. This section is played before hand in the piece, so I believe that when Beethoven repeated he wanted to emphasize it with the N6. The N6 also gives the piece a sense of suspense, and it allows the listener to question where/when the peice is going to resolve. I think Beethoven wanted to hold the listener's attention, and he does so by resolving the N6 to a major I. The major I also helps the piece transistion back into the well-known melody in the end. However, now it is heard in the bass.