As it reads in our translation, the term “because” seeks to provide an explanation for what the apostle wrote in 1 Peter 3:19. As it is, however, the term is not in the Greek and ought not to be in the translation; the rendering would instead be along the lines of “…to the spirits in prison, which formerly…”
20 because they formerly did not obey, when God’s patience waited in the days of Noah, while the ark was being prepared, in which a few, that is, eight persons, were brought safely through water.