Judah hath dealt treacherously, and an abomination is committed in Israel and in Jerusalem; for Judah hath profaned the holiness of the LORD which he loved, and hath married the daughter of a strange god.
Judah hath dealt treacherously - namely, in respect to the Jewish wives who were put away (Malachi 2:14; also Malachi 2:10; Malachi 2:15-16).
For Judah hath profaned the holiness of the Lord which he loved - by ill-treating the Israelites (namely, the wives), who were set apart as a people holy unto the Lord. "The holiness of the Lord" means "the holy seed" (Ezra 9:2: cf. Jeremiah 2:3, "Israel was holiness unto the Lord"). Or, "the holiness of the Lord" means His Holy ordinance and covenant, forbidding marriages with the pagan (Deuteronomy 7:3). But "which he loved" seems rather to refer to the holy people Israel, whom God so gratuitously loved (Malachi 1:2), without merit on their part (Psalms 47:4). Therefore the former explanation is preferable.
And hath married the daughter of a strange god - (Ezra 9:1-2; Ezra 10:2; Nehemiah 13:23, etc.)
The daughter of a strange god - i:e., women worshipping idols: as the worshipper in Scripture is regarded in the relation of a child to a father (Jeremiah 2:27, "Saying to a stock, Thou art my father"). The Jews, as Nehemiah found on his return to Jerusalem (Nehemiah 13:6), had "married wives of Ashdod, of Ammon, and of Moab."