New Defender's Study Bible Notes
40:3 a man. This “man,” with an appearance like brass, was surely an angel, indicating again that angels can take on the bodily form of men when God so directs. In fact, this may well have been a theophany, the “man” being the Son of God in pre-incarnate form (note Ezekiel 44:5).
40:3 line of flax. This “line” was flexible for approximate measurement of long distances, whereas the “reed,” or rod, was stiff, for accurate measurement of short distances.