This scene begins with Macbeth's soliloquy, in which the audience learns how torn he is about whether or not to go through with the assassination of King Duncan. Macbeth describes the prize awaiting him if he carries out the murder as a "poisoned chalice" and fears the "deep damnation" that would greet the murderer of such a good man as Duncan. Indeed, carrying out the murder would send "bloody instructions" to his people, who might follow his example in murdering him. This strong and evocative language evokes the real sense of foreboding and internal conflict Macbeth is experiencing.
His wife has no such qualms, or at least has managed to steel herself against them. She uses the strongest possible language to challenge Macbeth's masculinity and his honor in pushing him to commit the deed, saying that if she had promised to do such a thing, she would have "dash'd the brains out" of her own suckling baby before she went back on her vow. She then turns to phrases that are intended to arouse courage in her husband, encouraging him to "screw your courage to the sticking-place" and go through with it. The strong language used by both characters indicates the weight of the deed they are about to embark on.