Why does it say "Besulah" (singular)?
Radak: Every Besulah will rejoice.
Radak: "Besulah" refers to Keneses Yisrael.
Why does it say "Yachdav"?
Malbim: They will rejoice equally - unlike the building of Bayis Sheni, when the Zekenim cried greatly, because they remembered the honor of Bayis Rishon
What is "Sason"?
Malbim: It is Simanim done to show Simchah, e.g. wearing Yom Tov clothing. It is the opposite of external Aveilus, i.e. wearing mourners' clothing.
For what is the consolation?
Malbim: It is for the affliction they suffered in the past.
Why does it say "v'Simachtim mi'Ygonam"?
Malbim: I will rejoice them via their past agony. Remembering the past agony increases the current Simchah.
