He hath destroyed the works of the devil !

1 Jn 3:8

1 John 3:8
He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil.

The Lord Jesus Christ through His Death ALONE, hath destroyed the works of the devil, for those He died for. This was foretold eon's ago here Gen 3:15

15 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head [destroy], and thou shalt bruise his heel.

Yes the bruising of the serpent's [satan, the devil] head is exactly what Christ did accomplish Heb 2:14

14 Forasmuch then as the children are partakers of flesh and blood, he also himself likewise took part of the same; that through death he might destroy him that had the power of death, that is, the devil;

Now death has been abolished in regards to everyone Christ died for, and who is believing, and this is brought to light by the Gospel 2 Tim 1:9-10

9 Who hath saved us, and called us with an holy calling, not according to our works, but according to his own purpose and grace, which was given us in Christ Jesus before the world began,

10 But is now made manifest by the appearing of our Saviour Jesus Christ, who hath abolished death, and hath brought life and immortality to light through the gospel:

Those who are believing the Gospel of God's Grace, is evidence that Christ abolished Death on their behalf, that He destroyed the work of the devil regarding them. Now one of the symptoms of or effects of spiritual death and the devil's power over one, is Unbelief of the Gospel, for Unbelief is work of the Devil, scripture most certainly declares that 2 Cor 4:3-4

3 But if our gospel be hid, it is hid to them that are lost:

4 In whom the god[Satan] of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.

The lost natural man just simply cannot believe the Gospel and why ? "the god of this world hath blinded the minds of them which believe not," this is one of the works of the devil ! So yes, unbelief of the Gospel of God's Sovereign Grace is not believed by all those that the work of the devil prevails against. See Also Matt 13:19 ! He by spiritual death blinds their minds in unbelief ! But how so to those whom Christ has died for, and consequently hath destroyed the works of the devil ? I must testify, that it is impossible for anyone Christ died for, should remain in unbelief ! They shall one Day Live by Faith after having the Gospel Reveal to them the Righteousness of God Rom 1:16-17. Folks for if that could happen, that one Christ died for lives their whole Life in unbelief of the Gospel, if that happens, then the work of the devil prevailed against one for whom Christ died, he prevailed over His Victorious Death that should have destroyed his works, yes if one soul that Christ died for, dies in unbelief or is found in Gospel Unbelief when He returns, like these will be 2 Thess 1:8, then Christ's Death did not destroy the works of the devil. But alas, it is a fact, all those who do die in unbelief, or are in unbelief when Christ Returns, then Christ did not die for them, simple as that !