Answer:
It provides imagery so that the reader understands the severity of the weather conditions.
Step-by-step explanation:
Bolded text: "a pelting rain that stung like whip-lashes."
Or if you by some chance got "The waves beat upon the causeway and were carried across", that could be It specifies how far it is from the town to the causeway.
Or if u got "In water halfway to our waists" then It clarifies how deep the water was the character was wading in.
Or if you got " in utter darkness and numbed with cold, we groped our way toward the lights of the town scarce a hundred yards away." It compares the darkness to waves of rain. Or smth.
But the main answer is "It provides imagery so that the reader understands the severity of the weather conditions."