After showing the wrong way in 3.6, Krishna now reveals the right way. The true karma yogi controls the senses from within, using the mind as the reins, and then acts with the body — all without attachment to the results.
Two things work together here. First, inner control: the mind governs the senses rather than being dragged by them. Second, detachment: the work gets done, but the worker does not cling to the outcome. Like a skilled cook who prepares a feast for guests and takes joy in the cooking itself, not in the praise that may or may not follow. These two together — inner discipline and outer action without clinging — form the essence of Karma Yoga.