John Gill Commentary Ezekiel 21:1

"And the word of Jehovah came unto me, saying," — Ezekiel 21:1 (ASV)

Ver. 1. And the word of the Lord came to me, saying.
] Upon the Ezekiel 21:2

Son of man, set your face toward Jerusalem
Which shows that this city was meant by "the south", (Ezekiel 20:46).

and drop your word toward the holy places ; which also are meant by the south in the passage referred to, even the holy land, holy city, and holy temple; or the temple itself is only meant, with the courts adjoining to it; or as consisting of three parts, as Kimchi, the porch, the temple, and the oracle; or the outward court, the holy place, and the holy of holies; and it may respect all other places for sacred worship, as their synagogues, both in city and country; which were not to be spared any more than the temple, nor were they, (Psalms 74:7Psalms 74:8).

Jarchi thinks that the destruction both of the first and second temple is here intended; and which sense Kimchi also mentions.

And prophesy against the land of Israel :
by which it appears that this is intended by the "forest of the south field": even the numerous inhabitants of it in general, as well as the city of Jerusalem, (Ezekiel 20:46).