The Spirit of God through Noah preached about God and the punishment that was coming. They had been tried and convicted, as those in prison, but still God in His mercy waited 120 yrs. for them to change their minds and be reconciled to Him. But only Noah and his family believed and were saved.
Gen 6:3 And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.
Respectfully, I appreciate your explanation. I am familiar with the story of the flood and the ark. Forgive my saying honestly, the explanation that the Spirit of Christ was in Noah preaching righteousness is not actually being articulated in any of the verses below.
I note that the context is Christ's suffering once for sins, the just for the unjust, to bring us to God. This is the real thing and not a type. Hence dying in the flesh and then being brought back to life (quickened) seems to be about Christ's death and resurrection, however it's possible it could mean us who believe who were once dead in sins and now made alive. But the next verse seems to suggest it also was the means to preach to those "spirits" who were in prison which is a place Jesus (not us) went to. And the next verse qualifies those in this place he went to as being disobedient in the days of Noah.
Please understand I do not want to read into these scriptures more than what is there. Jesus died and rose. By which Jesus went somewhere. There he preached to spirits who were disobedient in the days of Noah. That is what I see despite viewing many conflicting interpretations.
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.