Charles Ellicott Commentary Isaiah 66:18

"For I [know] their works and their thoughts: [the time] cometh, that I will gather all nations and tongues; and they shall come, and shall see my glory." — Isaiah 66:18 (ASV)

For I know their works ... —The Hebrew has no verb, either—as in the Quos ego ... of Virgil, Æn., 1:1 39—for the sake of emphasis, or through an accidental omission in transcription. I know is supplied by many versions and commentators; I will punish or I have seen by others. The thought, in any case, is that the eye of Jehovah sees the evil things that are done in the secret places, caves or groves, in which the heathen rites were celebrated.

All nations and tongues ... —The phrase, though not incompatible with Isaiah’s authorship, is specially characteristic of the prophets of the Exile (Daniel 3:4; Daniel 3:7; Daniel 3:29; Daniel 4:1; Zechariah 8:23).

They shall come, and see my glory. —The “glory” in the prophet’s thoughts is that of Jehovah manifested in His righteous judgments on open enemies and concealed apostates.