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.
Apostles contemplate an informal remnant, promise judgment and a new thing, but hold out no present recovery. See 2 Timothy, 2 Peter, Jude, and Revelation 2 and 3.
Malachi's remnant were found by Jesus as Malachi left them. See Luke 1 and 2. So will the coming of the Lord find the saints as left by the apostles in the epistles.
So the Reformation in Christendom; the unclean spirits went out, but the house was not the Lord's.