Demons Can Change Their Functions:

The demon in I Kings 22:21-23 declared he would be a lying spirit. This indicates he was not one previously for he said "I will be...".

21 And there came forth a spirit, and stood before the Lord, and said, I will persuade him. 22 And the Lord said unto him, Wherewith? And he said, I will go forth, and I will be a lying spirit in the mouth of all his prophets. And he said, Thou shalt persuade him, and prevail also: go forth, and do so. 23 Now therefore, behold, the Lord hath put a lying spirit in the mouth of all these thy prophets, and the Lord hath spoken evil concerning thee. I Kings 22:21-23

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