The captivity did not purify Israel. The returned captives deny the love and despise the judgment of the Lord. See chapter 1:2; 2:17.
The unclean spirit went out; but the house was not the Lord's.
But there is a remnant, informal, spiritual, remembered now, to be distinguished hereafter.
They are exhorted to hold by the word. They are promised the judgment of the evil, and a new dispensation. They are not promised present recovery of David's throne or deliverance from the Gentiles.
So the Reformation in Christendom: the unclean spirit went out; but the house was not the Lord's.
Apostles contemplate an informal remnant, promise judgment and a new thing, but hold out no present recovery. See 2 Tim. 2 Peter, Jude, Rev. 2; 3
Malachi's remnant were found by Jesus as Malachi left them. (See Luke 1; 2) So will the coming of the Lord find the saints as left by the apostles in the epistles.