"How do I know if sinful thoughts are from me, or from the devil?"

That’s a deep question many believers have asked.

The short answer is this. Scripture doesn’t call us to spend much time tracing the source of a sinful thought so much as judging its nature, and responding accordingly. The Word of God gives us some light to speak carefully about the difference. So here it is in shorthand.

First, Scripture teaches that sinful thoughts arise from our fallen human nature. James says, “Every man is tempted, when he is drawn away of his own lust, and enticed” (James 1:14). The heart, even in the regenerate, still contains remaining corruption (Romans 7). Old sinful habits, memories, desires, and reflexes of the flesh surface without warning. The suddenness of a thought does not prove it is satanic, though it may be. The heart is a deep, dark labyrinth. Indwelling sin lurks in the shadows of the light, waiting for the right moment to attempt control.

Scripture also teaches that Satan actually does tempt, suggest, and provoke (Matthew 4:1–3; Luke 22:31; John 13:2). But he is not omniscient. He is not omnipresent. We need to understand that. He is called the tempter, yet he can’t possibly tempt every tempted person. Most are largely left alone because they are already his (John 8:44). Unless, of course, he is enlisting them in his war. Redeemed sinners on the other hand, will at times, face personal attacks from Satan’s daemons. His tactics are well known.

He casts fiery darts (Eph.6:16). He draws the heart away (James 1:14; 2 Cor. 11:3). He sifts as wheat (Luke 22:31). He accuses the brethren (Rev. 12:10; Zech.3:1). He disguises himself as an angel of light (2 Cor. 11:14) He seeks advantage through ignorance (2 Cor. 2:11). He snatches away the Word (Matt. 13:19). As the second greatest anthropologist in history, he has done his homework. He knows our weaknesses. So yes, the devil/s often works by way of thoughts that are foreign to new life, intrusive, blasphemous, even violent in their suggestion, especially when they happen during prayer or moments of spiritual seriousness. Yet the devil can’t sin for you. Your flesh is the dry tinder. Your lust is the gas. The devil presents the spark. There would be no fire if there were nothing to burn. He doesn’t create new material. He works with existing flesh.

So how do I know if sinful thoughts are from me, or from the devil?

The most important thing isn’t where the thought came from, but how you respond to it. When a thought enters, there is an incredibly brief moment where we either consent or resist. Is it welcomed, invited in, entertained? Is it embraced like an old lost friend? Then why does origin matter? It doesn’t. To be honest, if hell’s minions never visited me again, I would have all the tinder and gas I need to destroy myself. But on the other hand, a wicked thought that is resisted, fought against and wrestled into the light of the Son, is resisting sin. Regardless where it came from. Luther’s old line is so memorable, You cannot stop birds from flying over your head, but you can stop them from building a nest in your hair.

I would also add that your conscience gives an important clue. When a sinful thought arises, does your soul recoil? That response itself is telling. The unregenerate may grieve the effects and consequences of sin, but only the child of God grieve sin as sin. Especially in the face of so loving a Savior. Even then the believer may be horrified by thoughts he never chose and never wanted. That horror is the proof of grace (Romans 7:22,23).

Beware of over-scrupulosity. What I mean is don’t become trapped in constant inward looking, asking unbearably deep questions to yourself. This usually leads to paralysis of soul and unrelenting despair. Think of the man in the iron cage in Pilgrim’s Progress. Scripture does not teach an inward spiral. It calls us to watch, pray (as we heard last Lord’s Day), resist, flee, and fix our eyes on Christ. Whether the thought came from outside or inside makes no lasting difference. The remedy is the same. Humbled by sin, we are called to “Submit yourselves therefore to God. Resist the devil, and he will flee from you” (James 4:7). How do we resist? Through confessed need. Through faith. Through fresh dependence on the Spirit of Christ.

2 Corinthians 10:4, 5 
“For the weapons of our warfare are not carnal, but mighty through God to the pulling down of strong holds; Casting down imaginations, and every high thing that exalteth itself against the knowledge of God, and bringing into captivity every thought to the obedience of Christ.”

Finally, I hope you will remember this. Christ “was in all points tempted like as we are, yet without sin” (Hebrews 4:15). Temptation itself is not sin. Understand that clearly. When sin presents itself, it is not the first thought that matters most, it’s the second. Many of the most distressing thoughts believers experience are exactly the ones they hate and love the most according to Paul (Romans 7:15-24). “On second thought” should be our reply to temptation.

And one last thing, if the devil can’t win you to sin by temptation, he will accuse you for being tempted in the first place, turning warfare itself into false guilt. It is a merciless tactic.

So ask fewer questions about origin, and more questions about response.

Did I consent to this thought?

Did I welcome it?

Did I fight it?

Did I bring it to Christ?

And when the cry is as short and sweet as, “Help, Lord!” you may rest assured that grace was already working.