To pull out all the stops means to make a
great effort to achieve something. The origin came from organs.
Organ consoles have knobs that are called ‘stops’. Without them
the organist can play at a much higher volume, so ‘pulling out
all the stops’ would let the organist achieve maximum volume.
With all of the stops pushed in, there is no air movement, so
there is no sound. Strategically pulling out stops allows the
organist to influence the quality of the sound. Pulling out all
of the stops activates all of the pipe sets, so it results in a
very full sound, and maximum volume.