3:18 once suffered. For “once suffered,” a better connotation is “once for all died.”
3:18 quickened by the spirit. “Quickened by the Spirit” means “alive in spirit.” Although His body was in the tomb, His spirit (which could be understood as essentially the Holy Spirit, who is also called the Spirit of Christ), descended “into the lower parts of the earth” (Ephesians 4:9).
3:19 preached. While in Hades in the Spirit, He “preached”—that is, “proclaimed”—His victory over death and Hades (Matthew 16:18; Colossians 2:15; Revelation 1:18; Luke 4:18). Note that “hell” in these verses is the Greek hades, the great pit at the center of the earth where lost souls and many rebellious angels are confined. Before Christ’s resurrection, the souls of believers were also resting there, but these captives were delivered by Christ when He rose from the dead (Ephesians 4:8-10). The Greek word for “preached” here is not the word for “preached the gospel” (eyaggelizo) as in I Peter 1:12,25; 4:6, but rather kerusso, which means “proclaimed” (Luke 12:3) or “published” (e.g., Luke 8:39). Christ was not giving a second chance, as it were, to those who had died in unbelief, for there is no second chance after death (Hebrews 9:27). Rather, He was proclaiming victory over Satan and his hosts.
3:19 spirits. These “spirits in prison” almost certainly were the evil spirits who had sinned in the days of Noah by trying to corrupt and control all flesh (Genesis 6:1-4,12). Whenever the word “spirits” is used in the plural and not clearly indicated otherwise (as in Hebrews 12:23 and I Corinthians 14:32), it always refers to supernatural beings, or angels. In support of this meaning, note that there are thirty such occurrences in the New Testament, with only two, as noted above, referring to spirits of men. At least twenty-six of these thirty occurrences refer to evil spirits, which strongly indicates that to be the meaning here.
3:19 in prisons. The “prison” where these evil spirits are confined is identified elsewhere by Peter as tartarus, the Greek name translated “hell” in II Peter 2:4. This is evidently a special compartment of Hades where these “angels that sinned” are confined in “chains of darkness, to be reserved unto judgment.” They are also described in similar terms by Jude (see Jude 6).