Hear this word, you cows of Bashan,
  who are on the mountain of Samaria,
who oppress the poor, who crush the needy,
  who say to your husbands, ‘Bring, that we may drink!’
—Amos 4:1

Most people are flabbergasted when they discover that God regards contentious wives as cows. This is a hard thing for many people to understand, yet when the actions of these wives is compared to the excellent and virtuous wife of Proverbs 31, it is not such a surprise to see why God would regard the wives of Amos 4 as cows.

In Proverbs 31 it is King Lemuel’s mother who instructs her son of the virtues that identify a godly wife. These virtues include the wife’s desire and efforts to assist the poor and the needy:

She opens her hand to the poor
  and reaches out her hands to the needy.
—Proverbs 31:20

This is a stark contrast to the wives of Amos 4 who both oppress and crush the poor and needy. Instead of caring for those in need and loving their neighbors, they have taken upon themselves an attitude of selfishness, debauchery, and self-aggrandizement; audaciously insisting that their husbands serve their glutinous, rapacious, and epicurean appetites.

An excellent wife is one that puts the well being of her household before herself. She rises while it is yet night to prepare food for her household and portions for her maidens.

She rises while it is yet night
  and provides food for her household
  and portions for her maidens.
—Proverbs 31:15

She does not seek to indulge every passion and personal delight by devouring her increase, but with the fruit of her hands she plants a vineyard. She reinvests her profits into the future so that at a later time there might be feasting and thanksgiving with surplus and bounty.

She considers a field and buys it;
  with the fruit of her hands she plants a vineyard.
—Proverbs 31:16

Proverbs 31 sets forth the industrious woman who is regarded as a virtuous and excellent wife, while the self-indulgent woman of Amos 4 is rightly and justly regarded as a cow.