Before I get to nachamu, just a word about last week's haftarah of chazon because if I don't write this now I will forget by next year. In siman 282 in hil shabbos by the dinim of maftir the S.A. writes that if there is no one who knows how to read the haftarah except for someone who already got an aliya, that person is called up for maftir and says new brachos and reads the maftir pesukim even though he already got an aliya earlier. Achronim quote from the Rivash (see MB sk 26) an extension of this din that is a chiddush: On shabbos chazon even if there are multiple people in shul who can read the words and even lein the haftarah with the normal trop, that's not good enough -- only someone who can lein chazon with the trop of kinos can be called up for maftir, even if it means calling up someone who already got an aliya.
We see from here that the haftarah of chazon is not just a regular haftarah with a different tune -- no one says the din of the S.A. would apply at other times if there is someone who can read the words correctly but doesn't know the trop. It applies specifically to chazon because chazon is a kinah, and it has to be read as such. If not, then it's like not reading it at all.
Turning to this week, shabbos nachamu, the haftarah of nachamu. Hashem sends the navi to bring a message of nechama to Klal Yisrael.
ק֚וֹל אֹמֵ֣ר קְרָ֔א וְאָמַ֖ר מָ֣ה אֶקְרָ֑א (1:6)
There seems to be a shakla v'terya here, but it's not clear what's going on. Hashem is saying to call out to the people, and the response is "Mah ekra," what am I supposed to say? Metzudas David:
קול אומר קרא – קול נבואה אומר להנביא קרא והכרז ברבים.
ואמר – כאלו הנביא שואל מה אקרא
Hashem just said that the navi has to bring a message of nechama, so what's the question?
When do we give nechama? You do nichum aveilim after a person dies and is gone forever. Rashi (Brashis 37:35) writes that Yaakov Avinu could not accept nechama for the loss of Yosef because Yosef in fact was still alive. Chasam Sofer explains (in Toras Moshe at the end of Va'eschanan, and see Malbim for a different answer) that this is what bothered the navi. How can I give nechama for Klal Yisrael for the churban ha'bayis when the beis ha'mikdash is still alive for them? "Haysa k'almana" we read in Eicha -- "k'lamanah" with a kaf ha'dimyon because we are not really an almanah. We expect Hashem to come back to us, to come back to Yerushalayim, to rebuild the mikdash again. We are suffering but a temporary separation. For that, there is no nechama.
The answer Hashem gives is that the ultimate redemption will not simply be a restoration of what once was. "Yaveish chatzir naveil tzitz." That beis ha'mikdash of the past built by human hands is gone and will never be brought back. For that, Klal Yisrael needs and deserves nechama. "U'dvar Elokeinu yakum l'olam" -- there will be another mikdash built by Hashem's hands, and that mikdash will stand for eternity.