Complex sentence: The motor's armature current is supplied through the stationary brushes in contact with the revolving commutator, which causes required current reversal and applies power to the machine in an optimal manner as the rotor rotates from pole to pole.
Split into simpler sentences: The motor's armature current is supplied through the stationary brushes in contact with the revolving commutator, which causes required current reversal as the motor rotates from one pole to another. The commutator efficiently applies power to the machine as its rotor rotates from pole to pole.