His eyes are as flames of fire, Revelation 19:12 says. As fire separates the gold from the dross, so the eyes of this one will separate the righteous from the wicked and will discern the thoughts and the intents of the heart. He comes not only to war but to judge, and to judge perfectly. With these eyes He penetrates into the very heart and soul of every man. He sees what no one else can see. He looks upon the loves of the heart and the motives. He sees into the darkest corners where things have been covered up and hidden. He will judge with righteous, pure judgment.
Herman Hoeksema’s commentary on Revelation adds this to that description of the Lord that His eyes are as flames of fire, saying these eyes represent also the burning wrath in His bosom at this moment when He returns to judge those who have persecuted His church. The fires of His just wrath are stoked so high in His soul that it is as though the flames are flickering up and you can see them behind the retinas of His eyes.1
Cory Griess
12 His eyes are like a flame of fire, and on his head are many diadems, and he has a name written that no one knows but himself.