When Bathsheba arrives at the Corn Exchange in chapter 12 , her voice is said to be "as a romance after sermons." This simile helps to emphasize how different Bathsheba is from the rest of the people gathered in the Corn Exchange.
Indeed, Bathsheba is the only woman present. Comparing her voice to a "romance after sermons" implies that she brought to the room a lightness where before there was only heaviness and entertainment where before there was only ordinary routine. Another simile is used when her presence is described as "like a breeze among furnaces." In other words, Bathsheba's presence is like a breath of fresh air in a stale, hot room.
Hardy also uses language to emphasize, during this chapter, Bathsheba's femininity and sexuality. He refers, for example, to "her red mouth" and "parted lips." Her eyes are described as having a "softness," while also at the same time being "piercing." Bathsheba is, in short, "a woman in full bloom and vigor." This repetition or patterning of physical imagery is important because it emphasizes Bathsheba's femininity, which is, throughout the story, the cause of her greatest pains and her greatest victories. It is also, in chapter 12, her most conspicuous attribute from the perspective of those men gathered at the Corn Exchange.
When Farmer Boldwood appears, he is described as "a black sheep among the flock." This metaphor emphasizes how different Farmer Boldwood is from the rest of the men present. Indeed, later in the chapter he is described as "so wrapt up and indifferent, and seemingly so far away from all he sees around him." When every other man notices Bathsheba, Farmer Boldwood seems utterly indifferent, "as if Bathsheba and her charms were thin air." This last quotation is another example of a simile. Comparing Bathsheba's "charms" to "thin air" emphasizes how introspective Farmer Boldwood is.