أعذاره الساري العجول توقفا ما في وقوفك ساعة من بأس
Hold back the hurried night traveller; an hour's pause would do no harm.
The poetic wording presents a hurried night traveller and a call to halt. In the textbook's discussion, an earlier hemistich is brought into a new poetic scene; the image is made to fit the second composition.
When the scene concerns features appearing on a face, the relation between a restraint on travel and the new visual details becomes part of the literary effect. The borrowed words do more than repeat their earlier context.