“In that day.” 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 is similar to Isaiah 31:7.
“each person.” The Hebrew is singular. This will not be a collective action, but an action on the part of individuals.
“will cast away their idols.” There have been various reforms throughout history when people tried to get rid of idols, but they have at best been temporary and very limited in location. Furthermore, when all the “superstitions” that make things and actions into objects of respect and/or veneration, it can truthfully be said that idolatry has never been eradicated from human existence since the fall of Adam and Eve. This will change when Jesus reigns as king on earth. There will be no more idols. God will get the glory He deserves and the Shema, “Yahweh is our God, Yahweh alone” (Deut. 6:4), will be realized on earth. Other verses also give the same message as Isaiah 2:20, that idols will be gone (cp. Isa. 30:22; 31:7; Zeph. 1:4).
“idols.” The Hebrew text has the word 'eliyl (#0457 אֱלִיל), more literally “worthless ones,” a sarcastic name for “idols” (see commentary on Habakkuk 2:18, “worthless things”).