I think of the mind of the believer as being Satan’s playground. This is where he has the most fun and the most influence over you. Your heart is secure, God has won that already, but the damage that he can inflict on us through our thoughts is possibly immeasurable.
Satan is the father of lies, so his job is easy. He doesn’t have to get us to believe one particular thing, all he has to do is get us to believe anything but the truth. Really he doesn’t even have to get us to believe it either, merely doubt it. I heard a story once about Satan having a garage sale, and he was selling all kinds of tools of destruction. On one table he had items such as a brand new chainsaw for $25, some dynamite for $30, and other tools used for doing a lot of damage of reasonable price. On a separate table he had a well used steel wedge that he was asking $5000 for. The reason that the other tools were so much cheaper is that the victim can tell when he is under attack from one of those tools and can easily take steps to avoid or counter. Think of the average person being tempted to murder someone, probably not going to happen. The wedge on the other hand is used to separate incredibly strong bonds with minimal effort. I think of the conversation Eve had with the serpent. The serpent distorted the truth just enough and introduced doubt into her mind. Remember, Satan has been in the business of deception for thousands of years, and has tempted people an innumerable amount of times. I think he’s probably gotten pretty good at what he does.
1 Pet. 5:8 Be sober, be vigilant; because your adversary the devil walks about like a roaring lion, seeking whom he may devour.
He said "Believe Me"
10 months ago