John Gill Commentary Ezekiel 39:8

"Behold, it cometh, and it shall be done, saith the Lord Jehovah; this is the day whereof I have spoken." — Ezekiel 39:8 (ASV)

Behold, it is come, and it is done, saith the Lord God
That is, the salvation of his people, and the destruction of their enemies; the prophecy concerning all this is come to pass, and the whole is accomplished; thus, because of the certainty thereof, it is represented as if the time was actually come, and the thing was really done; for the event is as sure as if it was now fulfilled:

this is the day whereof I have spoken ;
by the Prophet Ezekiel and others; (See Gill on Ezekiel 38:17).