Haggai applies the priestly rulings and says, “So is it with this people… and so with every work of their hands” Haggai 2:14. He adds that what they offered there was unclean Haggai 2:14.
In Haggai 2:14–17, Yahweh applies a purity lesson to the whole community: they themselves, and therefore everything they do and bring, is treated as unclean. Haggai then urges them to look back over the period before rebuilding resumed, when their expected harvests repeatedly came up short. These verses sit inside Haggai’s fourth dated message (2:10–19). Just before this, Haggai asks the priests two questions about ritual transfer: holiness does not spread easily by contact, but uncleanness does (2:11–13).
Haggai 2:14–17 applies the priestly rulings about impurity (2:11–13) to the whole community. Yahweh declares that “this people” and “this nation” are unclean “before me,” and that this uncleanness reaches what they do and what they bring as offerings (verse 14).
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Haggai 2:14, then read the surrounding section so the answer stays connected to the passage's flow.
14Then Haggai answered, "`So is this people, and so is this nation before me,` says Yahweh; `and so is every work of their hands. That which they offer there is unclean.