Ezekiel 39:8

“Behold it comes and it will be done,” says the Lord Yahweh. “This is the day of which I have spoken.”

The uniqueness of this day comes out here. It is the final day of which Yahweh has spoken (Isaiah 2:12; Joel 1:15; Joel 2:1; Joel 2:11; Joel 2:31; Joel 3:14; compare Zechariah 14:1), in contrast with all the other ‘Days of Yahweh' on different nations occurring at different times, which are seen as foretastes of what is to come (Babylon  - Isaiah 13:1; Jeremiah 46:10; Lamentations 2:22; Zephaniah 1:1 to Zephaniah 2:3 in context with Ezekiel 2:4.  Edom  - Isaiah 34:1.  Israel  - Ezekiel 13:1; Amos 5:18 with 27). And all are assured that it will assuredly come.