Upon his resurrection (“made alive by the Spirit”) Jesus ascended into heaven (though in fact separated by forty days, the Scriptures more often compress the two events into one (Matthew 28:10, Matthew 28:16; Revelation 12:5). That going (“went”) was itself an (unspoken) “proclamation” of his victory over death, heard clearly by ungodly forces of darkness (“spirits in prison). Undoubtedly that proclamation was a cause of great distress to these imprisoned spirits; it implied they would never be released from their bondage.
18 For Christ also suffered once for sins, the righteous for the unrighteous, that he might bring us to God, being put to death in the flesh but made alive in the spirit,