“The prophets prophesy lies in my name.” It was a very serious sin to say that Yahweh said something that He did not say. Being a false prophet at all is a serious sin, but people who say that Yahweh, the God of Israel, told them to say something that He did not tell them to say are sinning very grievously. If a person says he is a prophet of Baal, God’s people can make a choice as to whether they want to listen or not, but if a person pretends to be a prophet of Yahweh, or says he represents Yahweh when he doesn’t, that requires a whole different level of diligence on the part of God’s people. People who say they represent God when they don’t are in danger of serious consequences, as Jeremiah 14:14-16 shows. Other verses that show false prophets prophesying in God’s name are Jeremiah 23:1-40, Jeremiah 28, Ezekiel 13:1-9 and 13:17-22.
“worthless divination.” The Hebrew text reads “divination and worthlessness,” which in this context is the figure of speech hendiadys (“hen-die-a-des”), in which two nouns are joined by “and” with the second noun acting as an adjective of the first. “Divination and worthlessness” become “worthless divination” by hendiadys. This gives us some insight as to the source of the information of the false prophets; at least some of it was coming from divination. Divination was an abomination to God (Deut. 18:9-14), and it gave the Devil plenty of ways to feed false information to the false prophets.