This sentence comes from Wang Anshi's poem "Xiang, excuse me, who gets the benefit of the Han Palace" in the Song Dynasty, which means that if one can control one's emotions and maintain inner peace, then three thousand kinds of troubles and pains can be eliminated. And "feelings are easy to kill two birds with one stone" means that emotions are easily affected by external factors, and once they are hurt, it is difficult to repair them.
My understanding is that a person can get rid of the troubled secular world only if he has peace of mind, and he is not easily hurt emotionally. For the handling of feelings, be cautious and calm, and don't waver easily, otherwise you will be hit by emotions like an arrow and get hurt soon. Only a peaceful mind can cure the pain and suffering caused by love.