In the last chapter Sun Tzu said soldiers driven into si di find strength instead. This chapter asks how that strength becomes the strength of a whole army.
Sun Tzu drew one who is good at using troops like this. He moves a whole army as though it were one person, held by the hand.
故善用兵者，攜手若使一人，不得已也
gu shan yong bing zhe, xie shou ruo shi yi ren, bu de yi ye
So one who is good at using troops directs the whole army as one person led by the hand, because he makes it so that nothing else is possible. (The Art of War, Nine Grounds, translated directly)