“And in many ways the animal method of doing things was more efficient and saved labour. Such jobs as weeding, for instance, could be done with a thoroughness impossible to human beings. And again, since no animal now stole, it was unnecessary to fence off pasture from arable land, which saved a lot of labour on the upkeep of hedges and gates. Nevertheless, as the summer wore on, various unforeseen shortages began to make them selves felt.” arable : fertile :: clouded : vague

In at least one hundred words, how does the analogy ("Arable is to fertile as clouded is to vague") help the reader to understand the meaning of the word arable in this excerpt?