Radak: In this vision, he saw another vision. Perhaps this is for the future in the days of Mashi'ach, like Yechezkel's visions in which an angel measured Yerushalayim, i.e. its length and width.

Malbim: He saw that the Ish will measure the length and width of the wall of Yerushalayim. This shows that the wall will be built soon, with Artachshasta's permission ? "v'Kav Yinateh Al Yerushalayim" (1:16).

Rashi (7): It was "ha'Mal'ach ha'Dover Bi" (7).

Radak: It was a different angel, not the one speaking to him.

Rashi: It is a measuring string to measure Yerushalayim ? what its length and width will be (6).