« In addition to the three haftarot of doom and the seven haftarot of consolation familiar to us, the Tosafot speak also of "two haftarot of repentance" belonging to this set of haftarot, namely Dirshu Hashem be-Himatzo that is read on Tzom Gedalya and Shuva Yisrael that is read this Shabbat. This means that this entire set of haftarot constitutes a response to Tisha be-Av.Torah on the Web - Virtual Beit Midrash
The destruction of the Temple necessitates a two-fold response: 1) mourning over the loss of the Temple and the members of Israel who fell in battle; and 2) a process of repentance "in order to stir up the hearts and open the paths of repentance. This should serve as a reminder of our own evil deeds and those of our forefathers that were as our present deeds to the point that they caused them and us these troubles, so that by remembering these things we should repent and do good."
The first and immediate response to the destruction is consolation; it is urgently needed in order to revive Israel's dejected spirit and strengthen their broken hearts. Following the great effort that was invested in this cause over the course of the summer, the time has come for the repentance that is required in the wake of the destruction as a repair of Israel's evil deeds that led to it. We see then that reading the haftara of Shuva stems from a double obligation of repentance: a) the special obligation of repentance generated by the Ten Days of Penitence; and b) an obligation of repentance in the wake of the destruction of the Temple, which is rooted in the laws of fasting, as is emphasized by the Rambam in the aforementioned passage. Formulated in a slightly different manner, it might be argued that now that we have finished reading the haftarot of consolation, the time has come to act toward their realization and bring about the redemption. This requires repentance and therefore we must deal with the issue of repentance in the haftarot that follow the haftarot of consolation.»