This Shabbos, the Shabbos following Tishah B'Av, is known as Shabbos Nachamu. It is named after the opening words of the Haftarah, "Nachamu, nachamu ami" ("Comfort, comfort My people").
The Haftarah is the first of seven readings called the "Shiva D'Nechemta," seven (Haftaros) of consolation.
The Levush (428:8) explains from this Shabbos until Rosh Hashanah that these Haftaros are read to console Klal Yisroel for the destruction of the Beis Hamikdash.
This Haftarah comes from Yeshayahu (40:1-26), and the Gemara Bava Basra (14b) tells us (according to the Maharsha), "Most of Yeshayahu speaks of consolation." This likely explains why all "seven haftaros of consolation" come from this book.