"[They cast what they have heard]" (meaning): the devils used to ascend to the heaven to listen, then they would descend to the soothsayers and inform them. The soothsayers would then relate what the devils had brought down, and the soothsayers would mix into it much falsehood, which they would then tell to the people. As for what was from the hearing of the heaven, it would be true, and [as for] what [was] mixed with it of falsehood, it would be a lie. "[And most of them are liars]" (meaning): their collective group.