Victorious Proclamation

For Christ also suffered once for sins, the righteous for the unrighteous, to bring you to God. He was put to death in the body but made alive in the Spirit. After being made alive, he went and made proclamation to the imprisoned spirits— to those who were disobedient long ago when God waited patiently in the days of Noah while the ark was being built... I Peter 3:18-20

To what spirits? Peter explains, a bit, that they were the spirits who almost destroyed the human race before the great flood. Jude gives us more in vs 6, about these angels who are incarcerated in a deep, dark place (chains of darkness, absence of light). Maximum security.
What proclamation? The same as to us: "IT IS FINISHED." His work of atonement was done. The victory has been won, and God has reclaimed His Own from the realm of Satan. This is the doctrine of Victorious Proclamation. There are so many technicalities involved in the Angelic Conflict that we (even saved) humans cannot completely grasp all that has been done for us, and in us, and through us. That is why we must walk by faith. In our eternal state we will understand this warfare, and our Lord's complete victory. Now, we must simply trust Him for His perfect provision and protection from the evil that seeks to destroy us. We are saved through the death, burial and resurrection of our Lord Jesus Christ, Who now represents us at the right hand of the Father. He is the Victor!