1)
Why does it say "Zeh ha'Davar"?
1.
Rashi: This is the end of the eradication of Mo'av via Nebuchadnetzar.
2.
Radak: This Nevu'ah was said about Mo'av many years ago, but the time [when it will be fulfilled] was not fixed. Now it was said, and the time was fixed.
3.
Malbim: This decree was on Mo'av from a long time ago, via early Nevi'im.
2)
From when is "me'Az"?
1.
Rashi #1: Yeshayah had this Nevu'ah many days before the evil came on him.
2.
Rashi #2: From when Balak hired Bil'am [to curse Yisrael].
3.
Refer to 16:13:1:2-3.