Commentaries:
Did the false prophets see a ghost? Did something cause them to have a dream? There is no indication of that. Because so many of them were involved—four hundred—it must be that the demon somehow stirred up the men's spirit and put the thoughts into their minds, making them think it was theirs. When they all came up with the same answer, surely it must have been right. But, alas, they were unanimously wrong, being led by a lying spirit.
We can see by this example that spirit beings can and probably are influencing mankind. It is not enough for us just to understand that they are capable of it. God's Word shows that they are actively doing it—good ones and bad ones—and some people are so unaware of what is going on that they give themselves over to the bad ones and become possessed—the slave, the tool, of a spirit being that will use them for its own ends. We are beginning to see established proof that Satan manipulates our minds.
John W. Ritenbaugh
Satan (Part 3)