The figurative language means the arrows were quickly shot. It impacts the description of Odysseus because it shows he is a skilled warrior.
Explanation:
Notice how carefully the words were chosen to convey this image: "poured out" and "rain of arrows". Picture that - you must have seen something similar in movies -, dozens of arrows falling from the sky like rain. For Odysseus to be able to do that, he would have to have great skills. He would have incredible aim as well as speed to cause the impression that arrows are raining down. This is what the author wants to achieve with the use of this figurative language. In a most eloquent and vivid manner, he conveys how skillful Odysseus is.
