are microscopic life forms that exist inside the cells of
all living things. While they are not the Force itself,
they form a link to it, acting as a sort of sensory organ
through which the Force can be perceived. Midi-chlorians
enable the perception of the Force just as having eyes allows
people to see light. Midi-chlorians are the connection between
a being’s mind and the Force, enabling certain sentiments
to intentionally manipulate it, or allow themselves to be
manipulated by it.
the midi-chlorians, life could not exist, and we would have
no knowledge of the Force. They continually speak to us,
telling us the will of the Force. When you learn to quiet
your mind, you'll hear them speaking to you."
Qui-Gon Jinn to Anakin Skywalker