There has been considerable misunderstanding of these verses of Scripture. It has been preached that Christ actually descended into the lower regions of the earth and preached to lost souls who were in prison in some type of purgatory or limbo. This is very far from what the text actually says. Let' s look at it closely now and get the real message of these verses. It says, "Christ also hath once suffered for sins ... that he might bring us to God, being put to death in the flesh, but quickened by the Spirit: By which also he went and preached."
First of all, notice how Christ preached to those spirits in prison. He did it by the Spirit, and that word is capitalised in your Bible. It actually refers to the Holy Spirit. So whatsoever Christ did in preaching during this period of time, He did it through or by the Holy Spirit.
With that in view, let's ask this: "When was the preaching done?" The answer is plainly given in verse 20: "when once the longsuffering of God waited in the days of Noah, while the ark was a preparing." So the preaching was actually done while the ark was being built--during the preaching of Noah to that antediluvian world. Now, one more question: "To whom was the preaching done?" The text says here "unto the spirits in prison." Throughout the Bible we find this terminology used in describing those who are bound in the prison house of sin. David prayed, "Bring my soul out of prison." Psalm 142:7. Paul spoke of his experience in these words, "bringing me into captivity to the law of sin." What Peter is telling us here is simply that Christ, through the Holy Spirit, was present while Noah preached; Christ was there through the Holy Spirit to speak conviction to their hearts and appeal to them to come into the ark. There is absolutely nothing in this text to indicate that Jesus left His body during the time He was dead to go to any subterranean place to minister to wicked spirits. The three questions are clearly answered in the text itself: (1) that He preached by the Holy Spirit, (2) He did it while the ark was preparing, and (3) He did it to the spirits in prison, or to those individuals whose sinful lives were bound in the prison house of sin.