1 Peter 3:18-20: (NASB1995) “For Christ also died for sins once for all, the just for the unjust, so that he might bring us to God, having been put to death in the flesh, but made alive in the spirit; in which also he went and made proclamation to the spirits now in prison, who once were disobedient, when the patience of God kept waiting in the days of Noah, during the construction of the ark, in which a few, that is, eight persons, were brought safely through the water.”

The “spirits” or spirit beings were the disobedient or fallen angels who materialized and married human women. This occurred during the days of Noah.  Genesis 6:1-4 (NIV), “When human beings began to increase in number on the earth and daughters were born to them, the sons of God saw that the daughters of humans were beautiful, and they married any of them they chose. Then the LORD said, ‘My spirit will not contend with humans forever, for they are mortal; their days will be a hundred and twenty years.’ The Nephilim were on the earth in those days–and also afterward–when the sons of God went to the daughters of humans and had children by them. They were the heroes of old, men of renown.” 

The “sons of God” were the angels who materialized. (Job 2:1 identifies angels as sons of God.) These spiritual sons of God left their heavenly home and materialized as human beings without God’s permission. This was against the Lord’s arrangements. Therefore, God deprived those angels of their liberties: “And the angels who did not keep their positions of authority but abandoned their proper dwelling (in heaven) – these he has kept in darkness (the demons cannot materialize but work in darkness including through witches, seances, etc.), bound with everlasting chains for judgment on the great day.” Jude 1:6 (NIV).  

The Apostle Peter also refers to them when he says, “For if God didn’t spare angels when they sinned, but cast them down to tartarus, and committed them to pits of darkness, to be reserved to judgment;” 2 Peter 2:4 (HNV). It was to these “spirits” that our Lord, by his life, his death and his resurrection, preached a powerful sermon through obeying God’s will.

Additional Resources:

Download PDF: “When a Man Dies”

Christian Questions Podcast – various audio episodes and study helps providing a scriptural walk-through of hell