He canceled the record of the charges against us and took it away by nailing it to the cross. In this way, he disarmed the spiritual rulers and authorities. He shamed them publicly by his victory over them on the cross. - Colossians 2:14
"Finished" is the word we use after a job is done. It is a word that says we don't need to work anymore, because it is done. "Finished" is also the word Jesus used from the cross. He said, "It is finished!" (John 19:30). In other words, "It is accomplished!"
The devil was soundly defeated at the cross of Calvary-and that is something he doesn't want us to know. Referring to His impending crucifixion, Jesus said, "The time for judging this world has come, when Satan, the ruler of this world, will be cast out." Through His death, Jesus destroyed the one who had the power of death, which is the devil. And when we put our faith in Jesus Christ, the stranglehold of Satan is broken. He cannot control us. We can rest in the finished work of Christ.
This means that when we face spiritual battles, we are not fighting for victory; we are fighting from it. We don't fight to get victory. We fight because it has already been obtained. We don't need to pray, "Lord, give me victory." Rather, we should pray, "Lord, I have victory, and I will live accordingly." As Romans 8:37 tells us, "Despite all these things, overwhelming victory is ours through Christ."
We can win in the spiritual battle. We can overcome the enemy. I am not saying we will win every skirmish and every conflict, but I am saying we will win the war. I am not saying we never will sin and never will stumble, because we will. We all will. But we can win the battle overall, because we stand in the righteousness of Christ.
So when the devil tries to strike that fatal blow against you, it no doubt will be repelled, because you are standing right with God.