<span>The supplicant creates a message digest by hashing the plaintext message. The verb to hash basically means to chop, meaning that you make something large into a smaller version. So, if you want to digest a message, meaning to shorten it, to summarize it, you will have to hash, or shorten the plaintext message. </span>
It slows the pace of the poem down to purposefully confuse the reader. It builds up anticipation about what will happen when the highwayman arrives. It helps to establish the setting of the town and the countryside.