Rodgers Organs with MIDI transmit more than just keystrokes. They also adjust the volume of the MIDI Module from the organ Expression Pedal and even the speed of the keystroke in many situations, so that the MIDI piano will have the sound that reflects the playing of the organist...and Brass may have the blaring attack on loud notes.
Aside from the owner's manuals for the organ and midi modules from Rodgers you may also be interested in the Frog Music Press Guides to playing the Organ and Playing MIDI Live. Both offer clear explanations and musical examples that teach you as you play through them.