Numeral 632 specifies that the first meaning given to this phrase has to do with the fact that Jesus, “before the resurrection, remained in the abode of the dead,” but “has descended as Savior proclaiming the good news to the spirits that were detained there.”
The next numeral, 633, explains what the Bible calls “hells; sheol or hades” to the abode “of the dead where Christ descended after his death, because those who were there were deprived of the vision of God.”
Christ then descended to that place “to free the righteous who had gone before him,” the good souls who were waiting for salvation and who can then go to heaven because with his death and resurrection, Jesus has opened the doors of paradise to them.