The phrase is implicated in a state of enlightenment of Zen mediation and compares words and meaning to a trap and a fish by implying that just as the trap exists because the fish, words exist because of meaning and once you have the meaning, you can forget the words.
「筌」とは魚をとるための道具で、前述の句は「目的を達すれば道具の存在を忘れる」という意味であり、禅の悟りの境地と結び付けられている。