What does John 18:6 mean?

When God revealed Himself to Moses, He identified Himself as "I Am" (Exodus 3:14). This summarizes God's nature as the only uncreated, eternal, always-existing being: He just is, because He must be. Seven times in the Gospel of John, Jesus pointedly used that same phrasing while claiming certain attributes of God (John 6:35; 8:12; 10:7, 11; 11:25; 14:6; 15:1).

Here, the claim is made as a blatant show of divine power. When a band of heavily-armed men arrived to arrest Him, Jesus actively engaged by asking who they had come for (John 18:4–5). His self-identification, recorded in the prior verse, literally knocks these men to the ground. Christ has always been clear that He knows what will happen, and is choosing to cooperate with God's plan (Matthew 20:18; John 12:32–33; 13:26–27). This moment highlights His sovereignty, reminding everyone that nothing happens to Him which is beyond His own control (John 10:17–18; Matthew 26:53).

Until now, Jesus has controlled both how and when He interacts with others. This overt demonstration of power is the last fully active deed in His earthly ministry. From this point forward, Jesus will submit to His own fallible creations as they condemn and murder Him (John 19:15–16).