“For in that day.” The subject shifts abruptly here, as is often done in the Old Testament. This is a common way of referring to the Day of the Lord, and this verse looks forward to the tribulation and kingdom of Christ on earth. This prophecy was not fulfilled at the end of the Babylonian captivity and is still future. This prophecy is similar to Isaiah 2:20.
“idols.” The Hebrew text has the word 'eliyl (#0457 אֱלִיל), more literally “Worthless Ones” or “worthless things,” a sarcastic name for “idols” (see commentary on Habakkuk 2:18, “Worthless Ones”).