The music video has a number of purposes, but its main purpose it to PROMOTE the single, the album the single is from and, of course, the artist. To do this, a music video has to;
1. Sell the song in a way that the audience can remember the song from the video
2. To provide the viewer with a better understanding of the song so they engage with it both visually and audibly (this is achieved through a performance or a 'story' telling)
3. to entertain the viewer by highlighting the talents of the artist - dancing, singing, performing and physical appearance