Having disarmed principalities and powers, He made a public spectacle of them, triumphing over them in it.

Colossians 2:15 NKJV

God has already given the believer victory in Christ Jesus. Jesus defeated Satan on the cross, in His death, burial and resurrection. Only doubt and sin defeats the believer in Christ.

Now with whom was He angry forty years? Was it not with those who sinned, whose corpses fell in the wilderness? And to whom did He swear that they would not enter His rest, but to those who did not obey? So we see that they could not enter in because of unbelief.

Hebrews 3:17-19 NKJV

When we don’t believe the Word of God concerning His promises, concerning the finished works of Christ, we deny ourselves the privilege of living in its reality. We are not able to walk in the fullness of it. We forfeit our inheritance in Christ Jesus. We live independent of it, we live outside of it.

When we live in sin, we expose ourselves to the devil and grant him the permission to do his works in our lives. Sin opens the door to Satan and permits him to function. It moves us out of God’s coverage of protection, makes us vulnerable to the enemy’s attacks and renders us susceptible to defeat.

The children of Israel suffered serious defeat in the hand of a small and not so powerful nation called Ai as a result of Achan’s sin. That’s how devastating sin is and when you couple that with unbelief, that’s just a double threat.