Why does it say "Tivtechu? El"?
Radak: An expression of Bitachon can be used with El, like here, or with Al, like in verse 8.
Who said "Heichal Hashem?"?
Radak #1: The false Nevi'im who deceive the people said so.
Radak #2: The people said so to Yirmeyah - Hashem will not destroy His Heichal and this city due to sins!
Why did they say "Heichal Hashem" three times?
Targum Yonasan, partially cited in Rashi: In front of Heichal Hashem you serve, in front of Heichal Hashem you sacrifice, in front of Heichal Hashem you bow. Three times a year you appear in front of Him!
Radak citing his father: They are three levels of Kedushah - the Ulam, the Heichal and the Devir (Kodesh ha'Kodoshim). "Eretz Eretz Aretz" (22:29) is the answer to their words - the Heichalos that you say in front of Me, they are considered [unimportant] to Me like the land, since you sin in front of Me and disgrace the Heichalos.
Radak: Perhaps it is repeated to strengthen the matter. This is often done; matters are repeated two or three times.
Malbim: Do not say that Heichal Hashem, since it was built l'Shem Hashem, it is Heichal Hashem. This is wrong. Your good ways and deeds, Hemah (they are) Heichal Hashem; [only] through them He will dwell in the Mikdash.
