Who is "the man" in Ezekiel 40:3 "He took me there, and I saw a man whose appearance was like bronze; he was standing in the gateway with a linen cord and a measuring rod in his hand."

Shalom, Thank you for your question. The commentators (Redak, and Metzudah David) explain that the man referred to in the verse is an angel from heaven, who appeared in the form of a man. This is similar to the angel who appeared to Jehoshua (Jos 5,13) “And behold a man was standing opposite him” - also an angel in the form of a man. Blessings.