1 John 4:1–6 Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world. This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God, but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming and even now is already in the world. You, dear children, are from God and have overcome them, because the one who is in you is greater than the one who is in the world. They are from the world and therefore speak from the viewpoint of the world, and the world listens to them. We are from God, and whoever knows God listens to us; but whoever is not from God does not listen to us. This is how we recognize the Spirit of truth and the spirit of falsehood.

 The greater one who is in you is Christ. He has already won the victory. “The
one who is in the world is Satan.” He tried to take control of this world away from Adam and Eve, something he had no right to do. But the crucifixion and resurrection of Jesus vanquished the devil. He knows his time is short and he is trying to wreak havoc in our lives. However, he cannot triumph over those who have Christ in them.

Luther wrote about this struggle this way:

Christ is stronger; He has overcome, is overcoming, and will overcome that strong man in us (Luke 11:21–22).” Still the devil does sometimes overcome us in the flesh, in order that even in this way we may experience the power of the Stronger against that strong man and say with Paul (2 Cor. 12:10): “When I am weak, then I am strong.” (Luther’s Works, vol. 26, p. 193, Concordia Publishing House, St. Louis).

He also addressed this in what may be his most famous hymn. Sing or read the words below, and concentrate especially on the words of the third and fourth stanzas.

A mighty fortress is our God, a trusty shield and weapon;
He helps us free from ev’ry need That hath us now o’ertaken.
The old evil foe Now means deadly woe;
Deep guile and great might Are his dread arms in fight;
On earth is not his equal.

With might of ours can naught be done, soon were our loss effected;
But for us fights the valiant One, Whom God himself elected.
Ask ye, “Who is this?” Jesus Christ it is.
Of sabaoth Lord, And there’s none other God;
He holds the field forever.

Though devils all the world should fill, All eager to devour us,
We tremble not, we fear no ill, They shall not overpower us.
This world’s prince may still Scowl fierce as he will,
He can harm us none, He’s judged; the deed is done;
One little word can fell him.

The Word they still shall let remain Nor any thanks have for it;
He’s by our side upon the plain With his good gifts and Spirit.
And take they our life, Goods, fame, child, and wife,
Though these all be gone, Our vict’ry has been won;
The Kingdom our remaineth.

(The Lutheran Hymnal #262)