The book of Haggai reminds exiles rebuilding Jerusalem and believers of every generation to remain faithful, obedient, and hopeful. One day God will return to establish a New Jerusalem.
Haggai challenges the returning exiles to remember their covenant, remain faithful to God and build the temple before constructing their own homes. While the new temple didn't meet their expectations, their efforts and faithfulness would be blessed. They could also be encouraged by God's promise to build a New Jerusalem for His international kingdom, defeat evil, and live in their midst. Future prophetic books contain more details about when these promises would be fulfilled.