What does John 8:9 mean?
Of all of Jesus' responses to His critics, this seems to be the most dramatic. Typically, those who challenged Jesus (Matthew 16:1; 19:3; Matthew 22:35; Luke 10:25; 11:54) were simply foiled, or frustrated. In this case, they're driven off entirely. The Pharisees have attempted to trick Jesus by challenging Him to stone a woman caught in adultery. However, they have not followed the entire law. The guilty man is not present (Leviticus 20:10; Deuteronomy 22:22), they are not planning to begin the execution themselves (Deuteronomy 17:7), and they seem to have no appreciation for God's sense of mercy (Deuteronomy 4:31; Psalm 145:8).When Jesus writes on the ground and challenges their approach, the men turn and leave. Not only do they fail to ruin Jesus' reputation with the people, they actually make Him look even wiser, and themselves even less holy.
The phrasing here can be interpreted to mean that Jesus and the woman are literally the only two people in this area. However, the context strongly suggests that Jesus and the woman are only alone "in the midst" of the crowd, now that the Pharisees have left. In other words, once the accusers are gone, all that is left in front of the crowd are Jesus and the adulterous woman.