18 For Christ also hath once suffered for sins, the just for the unjust, that he might bring us to God, being put to death in the flesh, but quickened by the Spirit: 19 By which also he went and preached unto the spirits in prison; 20 Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water.
...1 Pe 3:18-20
The Holy Bible : King James Version. electronic ed. of the 1769 edition of the 1611 Authorized Version. Bellingham WA : Logos Research Systems, Inc., 1995, S.
there is a seminary level commentary on it...
"3:19-20. Through whom . . . He . . . preached to the spirits in prison has been subject to many interpretations. Some believe Peter here referred to the descent of Christ’s Spirit into hades between His death and resurrection to offer people who lived before the Flood a second chance for salvation. However, this interpretation has no scriptural support.
Others have said this passage refers to Christ’s descent into hell after His crucifixion to proclaim His victory to the imprisoned fallen angels referred to in 2 Peter 2:4-5, equating them with “the sons of God” Moses wrote about (Gen. 6:1-2). Though much commends this view as a possible interpretation, the context seems more likely to be referring to humans rather than angels.
The “spirits” (pneumasin, a term usually applied to supernatural beings but also used at least once to refer to human “spirits”; cf. Heb. 12:23) are described in 1 Peter 3:20 as those who were disobedient when God waited patiently for Noah to finish building the ark. They had rebelled against the message of God during the 120 years the ark was being built. God declared He would not tolerate people’s wickedness forever, but would extend His patience for only 120 more years (Gen. 6:3). Since the entire human race except Noah (Gen. 6:5-9) was evil, God determined to “wipe mankind . . . from the face of the earth.” The “spirits” referred to in 1 Peter 3:20 are probably the souls of the evil human race that existed in the days of Noah. Those “spirits” are now “in prison” awaiting the final judgment of God at the end of the Age.
The problem remains as to when Christ preached to these “spirits.” Peter’s explanation of the resurrection of Christ (3:18) “by the Spirit” brought to mind that the preincarnate Christ was actually in Noah, ministering through him, by means of the Holy Spirit. Peter (1:11) referred to the “Spirit of Christ” in the Old Testament prophets. Later he described Noah as “a preacher of righteousness” (2 Peter 2:5). The Spirit of Christ preached through Noah to the ungodly humans who, at the time of Peter’s writing, were “spirits in prison” awaiting final judgment.
This interpretation seems to fit the general theme of this section (1 Peter 3:13-22)—keeping a good conscience in unjust persecution. Noah is presented as an example of one who committed himself to a course of action for the sake of a clear conscience before God, though it meant enduring harsh ridicule. Noah did not fear men but obeyed God and proclaimed His message. Noah’s reward for keeping a clear conscience in unjust suffering was the salvation of himself and his family, who were saved through water, being brought safely through the Flood."
Walvoord, John F. ; Zuck, Roy B. ; Dallas Theological Seminary: The Bible Knowledge Commentary : An Exposition of the Scriptures. Wheaton, IL : Victor Books, 1983-c1985, S. 2:851-852
