Hebrews 2:14 ESV
Since therefore the children share in flesh and blood, he himself likewise partook of the same things, that through death he might destroy the one who has the power of death, that is, the devil.
Jesus became one of us so that on our behalf he could destroy the claim death had on us. Sin brings death so because we all have sinned, death was our unavoidable destiny. But Jesus paid the price to forgive us. Therefore we who believe no longer face eternal death. Instead we have eternal life.
Jesus destroyed the devil in that he destroyed his power to make us sin. And he destroyed the devil in that he can no long insist that we pay the price for our sins. If we are trusting Jesus as our Savior, have repented, and are living for him, the devil is destroyed regarding his power over us.