1)
It does not say to whom was Devar Hashem!
1.
Radak: It was to me (Zecharyah). There is nothing like this in Tanach.
2)
What is the purpose of this Dibur?
1.
Malbim: Above informed them that fasting will not fix the past and turn back Hashem's anger. Yerushalayim was destroyed for not heeding the Nevi'im - this cause must be removed! Now it arouses them that it is possible that this Bayis will be supreme, and the Shechinah will return and all exiles will return, if they will do Mishpat and Tzedakah.
