Why does it say "Chalonei" and not Chalonim? This word is not Samuch!
Radak: It is as if says Chalonim. We find like this - "Nit'ei Na'amanim" (Yeshayah 17:10, is like Neta'im), "Anshei Mechukeh" (Yechezkel 23:14) and many others.
What is the meaning of "Shekufim Atumim"?
Rashi, citing Menachos 86b: Shekufim is an expression of seeing and opening. The windows (openings in the walls) were open on the outside and closed on the inside. I.e. the opening was smaller inside, unlike other windows which are made for light to enter. This showed that Hashem did not need light from the outside. Malbim - even though one who stands outside sees wide windows, and it looks like He needs the light of day [to enter], one who stands inside sees the light of the Shechinah shine there, and Hashem's light illuminates with His honor.
Radak citing Targum Yonasan: Open on the outside and closed on the inside. Poles cover where the ends of the cedar beams are placed [in the walls].
Gra: They were open, with doors, so it was possible to close them.
Malbim citing Mahari: They were Shekufim and Atumim via a glass. 1
I.e. there was a one way glass (mirror) that allowed light to leave, but not to enter. (PF)
