Lessons.GregGoad.net
It is the bridge between the percussive part of the music and the all of the melody and harmony that is happening. As the bass player, you are the conduit in which the drums and the guitar communicate.
The bass also frames the perspective at which the harmonies are heard from. Humans hear sound from the lowest pitch upward. The bass controls this lowest note: and so as the bass player you wield a tremendous amount of power. You can change one note, and change the band from sounding happy to sad. When you stop playing, the whole room will hear it.