Malbim: The vision that began with Chagai and Zecharyah in Daryavesh's second year, when they began to build the Beis ha'Mikdash, it was sealed that year. They did not have another vision from Hashem, for it was not the time for Shechinah and Nichush to return to Yisrael. In the fourth year, Hashem spoke to him for the reason that will be explained. "Hayah Devar Hashem" - after it had ceased.