In this character interaction, the two characters have warring motivations. The soothsayer wants to warn Caesar again; this is evidenced by his statements, "I shall beseech him to befriend himself," meaning to protect himself. When he says, "I'll get me to a place more void and there/Speak to great Caesar as he comes along," we find that the soothsayer wants to get Caesar alone, probably because he doesn't know who around him can be trusted. Conversely, Portia wants Brutus to succeed in his assassination of Caesar. When the soothsayer tells her he is going to warn Caesar to protect himself she replies, "Why? Know'st thou any harm's intended towards him?" to find out what he knows. By her lines "O Brutus,/The heavens speed thee in thine enterprise!" we see that she wants him to hurry and commit the act before Caesar can be warned.