1)
What is "Kol Beis ha'Gadol"?
1.
Rashi (citing Megilah 27a) #1: It is Batei Kenesiyos, in which they Megadel (grow) Tefilah.
2.
Rashi (citing Megilah 27a) #2: It is Batei Midrash, in which they Megadel Torah.
3.
Radak (Melachim II, 25:9, citing Targum Yonasan): It is every house of a great person.
