Jesus’ descent into hell means that Jesus “sojourned in the realm of the dead prior to his resurrection” (the Catechism 632). Like all men, Jesus experienced death, and thus his soul joined others in this realm. But as the Catechism points out, “he descended there as Savior” (CCC 632) and preached the good news to the spirits imprisoned there (1 Pet. 3:19).
Does this mean Jesus descended into hell to deliver the damned? Does this mean Jesus destroyed the hell of damnation? No. Scripture often uses the term hell—Sheol in Hebrew and Hades in Greek—to refer to the abode of the dead, which consisted of both the righteous and the unrighteous who were deprived of the vision of God.
But this doesn’t mean their experience of that realm was identical. Jesus made this clear in his parable of the poor man and Lazarus (Luke 16:22-26). The Jews affectionately referred to the righteous abode as “Abraham’s bosom.”
It is these spirits to whom Jesus preached the good news. “It is precisely these holy souls, who awaited their Savior in Abraham’s bosom, whom Christ the Lord delivered when he descended into hell” (CCC 633).
For more, see “The Afterlife of the Old Testament Just Souls.”