Albert Barnes Commentary Judges 6:17

"And he said unto him, If now I have found favor in thy sight, then show me a sign that it is thou that talkest with me." — Judges 6:17 (ASV)

A sign - If the Angel partook of Gideon’s present it would be a conclusive proof of the reality of the vision. (Luke 24:37–43; Acts 10:41.) It would also be a token of God’s goodwill to Gideon. Compare Genesis 18:3.