"Nachamu Nachamu Ami" (Yeshayahu 40:1). Am Yisroel sinned doubly (Eicah 1:8), was punished doubly, and is consoled doubly (Psikta, Nachamu). What is the nature of the double sin and consolation? Yeshayahu said "for she has received double [punishment] for all her sins from the hand of Hashem (Yeshayahu 40:2)" - what is the justification for Am Yisroel being punished doubly for its sins?
Am Yisroel is fortunate! When we comply with Hashem's will, no nation can rule over us; when we don't comply, He places us in the hands of "lowly nations and even its animals" (Kesubos 66b). The Maharal explains that our lowliness when we sin is also part of our being fortunate, in that it emphasizes that we cannot be average - either we rise above others, or we sink beneath them (Netzach Yisroel ch. 14). If our descent starting at the churban Beis Hamikdosh merely equated us with other nations, this would indicate that our status in Hashem's eyes is no different than theirs, and that the Torah is merely a tangential, not fundamental, dimension of our existence. Our inability to be on par with other nations indicates that Torah is an intrinsic, indispensable part of our very existence. Torah and Yisroel are one, and thus we are very fortunate (Rav Chaim Yaakov Goldwicht zt"l).
Perhaps, then, the double sin is that we sank two levels: from above the other nations, to below them; from a lofty roof to a deep pit (Chagiga 5b, based on Eicha 2:1). While the inability of Am Yisroel to be on the level of other nations is in fact a sign of Hashem's love, it also results in our sins being doubled, as we sink two levels, not just one, when we falter. We are thus punished doubly, for the two descents, but we are also consoled because Hashem created us uniquely, and the double punishment is a sign of His love.
This lesson provides a measure of consolation even when we are in galus. One who mourns over Yerushalayim is privileged to see its joy (Ta'anis 30b). Mourning over our double descent reminds us that we can and will rise from the pit to great heights, and this consoles us with a vision of a joyous future. When that future arrives, there will be a double consolation, "nachamu nachamu".
Yirmiyahu foresaw the destruction of the second Beis Hamikdosh (Rashi, Eicha 4:21), and declared: "Hashem will not exile you again" (4:22) after the galus of Edom (Rashi). The cities of Eretz Yisroel are in a state of destruction when other nations rule over them (Magen Avraham 561:1). Today, when Am Yisroel rules over the Eretz Yisroel, we are promised that there will be no future exiles (B'ikvei Hatzon, p. 214, 215, based on Ramban Vayikra 26:16).
The promise that we will not have any more exiles enhances for us the consolation that mourners over Yerushalayim experienced throughout the generations. May this consolation give us strength to endure the difficult situation of Am Yisroel in Eretz Yisroel and in the galus, and may it soon be joined by the consolation of the ultimate redemption, when the navi's double expression, "nachamu nachamu ami", will be fulfilled.