Haggai encourages those who have just returned from exile to remain faithful, obedient, and hopeful for God's promise of 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 will be blessed. They can be encouraged by God's promise to build a new Jerusalem, defeat evil, and live in their midst. Future prophetic books contain more details about when these promises will be fulfilled.