1 Peter 3:19 By which also he went and preached unto the spirits in prison

This passage is often thought to refer to dead spirits in hell. But that would be a major contridiction to many other teachings.

The context of this passage falls within a teaching by Peter concerning the conscience. It is in regard to suffering for righteousness sake (verse 14), as did Noah while building the ark. Looking ahead to the next passage, we find that this preaching occurred in the days of Noah. Now, if we combine these facts with 2 Peter 2:5, where Noah is described as "a preacher of righteousness", the pieces should begin to come together.

2 Peter 2:5 And spared not the old world, but saved Noah the eighth [person], a preacher of righteousness, bringing in the flood upon the world of the ungodly;

The word “prison” could mean “in watching” or “keeping watch”. Therefore, the "spirits in prison" should be understood as the spirits who watched Noah, as he built the ark, and who presecuted him for doing the works of God. Looking back to verse 17, we can now see how Noah fits into Peters teaching regarding the suffering for well doing.

As the pieces come together, we can see that Christ went and preached to those who persecuted Noah, while they sat by and watched him build the ark. Christ preached to these souls in the same way He preached to many throughout the Old Testament, through a prophet who was moved by the Holy Ghost (2 Peter 1:21).