This is Epictetus' way of saying "the obstacle is the way."
It is possible to benefit from every circumstance, "even abuse and slander."
"A boxer derives the greatest advantage from his sparring partner - and my accuser is my sparing partner. He trains me in patience, civility and even temper."
"... a doctor who puts me in a headlock and sets a dislocated pelvis or shoulder - he benefits me, however painful the procedure. So too does a trainer when he commands me to 'lift the weight with both your hands' - and the heavier it is, the greater the benefit to me."
"I have a bad neighbor - bad that is, for himself. For me, though, he is good: he exercises my powers of fairness and sociability. A bad father, likewise, is bad for himself, but for me represents a blessing. The wand of Hermes promises that 'whatever you touch will turn to gold'. For my part, I can say, 'bring what challenge you please and I will turn it to good account: bring illness, death, poverty, slander, a judgement of death: they will all be converted to advantage by my wand of Hermes.'"
Be sure to check this post out: http://www.rockyrook.com/2017/09/commentary-on-meditations-b58.html and watch the video of Johnny Cash's song Sue.