Both poetic endings are important because the core meaning survives without them, yet the final words add a new feature.
Closing wordingRhetorical contribution
fī raʾsihi nārIntensifies the prominence of the guide
alladhī lam yuthqabMakes the eye–onyx comparison more exact
Exaggeration is not required in every instance. Refinement of a simile can itself justify a poetic closing. This variety shows why iṭnāb must be assessed through its specific benefit.