For for this cause was the gospel preached also to them that are dead, that they might be judged according to men in the flesh, but live according to God in the spirit.(1 Peter 4:6) KJV
In making the case that Jesus was the one who preached to the dead the very first issue that we have to deal with is: what does dead mean? How can someone who’s dead listen to preaching?
Alive or dead isn’t as simple as we would like it to be. It’s not merely a matter of whether or not our bodies are functioning vs. the cessation of metabolic activity. We can be biologically alive at the same time as being spiritually dead. We can also be both biologically and spiritually dead but still conscious, aware of our environment and receiving stimuli. This is because our consciousness is contained in a gravity node. It’s not the brain, even though it uses the brain to control the body to interact with the environment.
The word alive has some Biblical synonyms. Dead is the opposite of alive and it also has synonyms. Here’s a summary.
Alive or Dead?
If Jesus is descending into the lower parts of the Earth, the lower mantle, to preach to the dead spirits in prison, then he’s addressing the dead who are confined in the pit, which is also referred to the lowest hell and is the functional equivalent to the molten core of the Earth.
This is similar in a way to the parable of the rich man and Lazarus in Luke 16:19-31, when Abraham, who was in a chamber in the lower mantle, gave a mini-sermon explaining to the rich man, who was in the molten core, that there was more than enough testimony for his brothers to be able figure out how to avoid ending up in the fire.