The reason your instructor was making you practice techniques repeatedly hard (go), and soft (ju) is because you must repeat each movement, strike, and counter in Goju practicing it this way seperately so that ultimately you will be able to combine these two ways so that every technique is, "Goju". for example when executing a punch you will have great speed in the first part of the punch and in the last bit of the punch you will have the power to delivery a knockout blow.