The haftorah for Shabbos Hagadol is the concluding parsha in Trei Osor. When Shlomo Hamelech built the first Beis Hamikdosh, he already knew that it would be destroyed. According to the pessukim in Tehillim (106) and Yechezkel (23), Bnei Yisroel were already told right after the cheit hameraglim that the Beis Hamikdosh that they will build in Eretz Yisroel in the future would be destroyed and the nation would be sent into galus. (See the commentary of the Netziv to Parshas Shlach (14:21).) Shlomo Hamelech wrote in Shir Hashirim, regarding the second Beis Hamikdosh which will be built after the seventy years of galus Bavel, that if the entire Jewish nation would return en masse to Eretz Yisroel then the new Beis Hamikdosh would be like a metal structure which would not rot away. If, however, the aliyah at the end of the galus Bavel would be weak, then the second Beis Hamikdosh would be like a wooden hut which would rot away. The Gemorah (Yoma) understands this rotting away in a double sense: first, that the Beis Hamikdosh would be destroyed, and second that the Jewish people would rot away because Hashem would not send any more nevi'im.
The aliyah from Bavel in the days of Ezra and Nechemia was so weak it was obvious from the very start that the second Beis Hamikdosh would not last. After the return from galus Bavel there were only three nevi'im: Chaggai, Zecharia, and Malachi. Because the halacha states that one may not build a Beis Hamikdosh without express authorization from a novi, each one of the three nevi'im gave instructions about different aspects of the construction of the Beis Hamikdosh. In this final chapter in the nevuah of Malachi, he warns the people that they better observe the laws in the Torah. The role of the novi is to give mussar and tochacha, and Hashem will not be sending any more nevi'im. Malachi says that he is the last novi until Eliyahu Hanovi who will only come a day before moshiach. At that time there will be a tremendous teshuva movement. We wait every day with baited breath for the appearance of Eliyahu Hanovi which will lead to the yemos Ha'moshiach.