What does a Christ Follower have in common with a demon? They are both in agreement of God’s existence; that there is one God. In James 2:19, we read, “You believe that God is one. You do well; the demons also believe, and shudder.”
Add Matthew 7:20 – 24, “Wherefore by their fruits you shall know them. Not every one that says to me, Lord, Lord, shall enter into the kingdom of heaven: but he that does the will of my Father who is in heaven, he shall enter into the kingdom of heaven. Many will say to me in that day: Lord, Lord, have not we prophesied in your name, and cast out devils in your name, and done many miracles in your name? And then will I profess unto them, I never knew you: depart from me, you that work iniquity. Every one therefore that hears my words, and does them, shall be likened to a wise man that built his house upon a rock.”
It seems as though there is an unsaving knowledge of God. That is, there is a difference between an intellectual assent only (which could lend itself, as in the case of those pleading their case in the passage from Matthew, to creating false believers) and volitional commitment that is indicative of authentic salvation. The demons had a different story but they knew; still know, most assuredly, of God’s existence.