Jamieson, Fausset and Brown on Revelation 1:15

15. fine brass--Greek, "chalcolibanus," derived by some from two Greek words, "brass" and "frankincense"; derived by Bochart from Greek, "chalcos," "brass," and Hebrew, "libbeen," "to whiten"; hence, "brass," which in the furnace has reached a white heat. Thus it answers to "burnished (flashing, or glowing) brass," Eze 1:7; Re 10:1, "His feet as pillars of fire." Translate, "Glowing brass, as if they had been made fiery (red-hot) in a furnace." The feet of the priests were bare in ministering in the sanctuary. So our great High Priest here.

voice as ... many waters--(Eze 43:2); in Da 10:6, it is "like the voice of a multitude." As the Bridegroom's voice, so the bride's, Re 14:2; 19:6; Eze 1:24, the cherubim, or redeemed creation. His voice, however, is here regarded in its terribleness to His foes. Contrast So 2:8; 5:2, with which compare Re 3:20.