Albert Barnes Commentary Ezekiel 40:3

"And he brought me thither; and, behold, there was a man, whose appearance was like the appearance of brass, with a line of flax in his hand, and a measuring reed; and he stood in the gate." — Ezekiel 40:3 (ASV)

The appearance of brass - Brightly shining.

A line of flax - For measuring the ground plan.

A measuring reed - For the walls . To measure implied a separation for sacred purposes. The measurements are:

1. Exact, to show that the promise is certain;
2. Equal, to denote harmony;
3. Vast, to mark majesty and grandeur.