It was by the Holy Spirit that He went to preach [See Eph. 2:17] to the [now departed] spirits [of pre-Flood people who are now] in prison [i.e., Hades].

These people had disobeyed [Noah's preaching, See II Pet. 2:5] back when God's patience waited [for them to repent, See Gen. 6:3], during the days of Noah, when the ship was being constructed. It was by that means [i.e., the ship floating them to safety through the Flood waters] that a few persons, eight of them, were saved [from destruction] through water.