"He also went and made a proclamation to the spirits in prison." -1 Peter 3:19
The “spirits in prison” are mentioned in the context of what Jesus did in time between His death and resurrection. We know four things about the spirits referred to in 1 Peter 3:19. The Spirits are:
• Incorporeal (without a physical body)
• committed sin before the Flood
• were visited by Jesus at the place of their captivity to make an announcement to them.
Who exactly these spirits are has been the subject of some speculation through the years. The verse proclaims Christ’s victory over demonic spirits after his death and resurrection.
First, let’s look at the word spirits. It is a translation of the Greek word pneumasin, a form of the word pneuma, which means “air, breath, wind.” The Greek word for spirits is used in the New Testament almost certainly refers to angels (Hebrews 1:14). “Spirits” (pneumata) in the plural almost without exception in the New Testament refers to angels. While the Bible makes it clear that human beings possess a spirit (Hebrews 4:12), the Bible never refers to people as merely “spirit.” In contrast, God the Holy Spirit, angels, and demons are never said to possess spirits; they are spirits. So the usual meaning of the word spirits in the phrase spirits in prison argues for the spirits’ being something other than human beings.
The spirits in prison cannot be the holy angels because they have not sinned and are not imprisoned. And, if the spirits in prison are not the spirits of deceased human beings, that leaves us with one option—the spirits in prison are demons. Now, it is clear that not all the demons are imprisoned. The New Testament gives many examples of demonic activity on earth. So the spirits in prison must be a select group of demons who, unlike the rest of their demonic allies, are held captive.
What might be a reason for some, but not all, of the demons to be imprisoned? Jude 1:6 gives us an important clue. Some fallen angels committed egregious crimes of some kind causing them to be locked away. Jude 1:6 does not provide details, but the demons’ sin was related to how they “did not keep their position but deserted their proper dwelling.”. Revelation 9:1–12, 14–15, and 2 Peter 2:4 also speak of a group of very wicked angels that are currently bound.
The sin the spirits in prison committed could be referenced in Genesis 6:1–4, which records the “sons of God” mating with the “daughters of men” and producing a race of giants, the Nephilim. If the “sons of God” were fallen angels, then the sin of Genesis 6 involved angels leaving the place where they belonged in the act of disobedience before the Flood—and that corresponds to what the apostle mentions in 1 Peter 3:19. It seems likely that the demons who cohabited with human women were imprisoned by God to prevent them from repeating that sin and to discourage other demons from trying it.