CATECHISM OF THE CATHOLIC CHURCH
SECOND EDITION

Paragraphs 622–626

622 The redemption won by Christ consists in this, that he came "to give his life as a ransom for many" (Mt 20:28), that is, he "loved his own to the end" (Jn 13:1), so that they might be "ransomed from the futile ways inherited from their fathers" (1 Pt 1:18).
623 By his loving obedience to the Father, "unto death, even death on a cross" (Phil 2:8), Jesus fulfills the atoning mission (cf. Is 53:10) of the suffering Servant, who will "make many righteous; and he shall bear their iniquities" (Is 53:11; cf. Rom 5:19).
624 "By the grace of God" Jesus tasted death "for every one". In his plan of salvation, God ordained that his Son should not only "die for our sins" but should also "taste death", experience the condition of death, the separation of his soul from his body, between the time he expired on the cross and the time he was raised from the dead. The state of the dead Christ is the mystery of the tomb and the descent into hell. It is the mystery of Holy Saturday, when Christ, lying in the tomb, reveals God's great sabbath rest after the fulfillment of man's salvation, which brings peace to the whole universe.
625 Christ's stay in the tomb constitutes the real link between his passible state before Easter and his glorious and risen state today. The same person of the "Living One" can say, "I died, and behold I am alive for evermore":

God [the Son] did not impede death from separating his soul from his body according to the necessary order of nature, but has reunited them to one another in the Resurrection, so that he himself might be, in his person, the meeting point for death and life, by arresting in himself the decomposition of nature produced by death and so becoming the source of reunion for the separated parts.

626 Since the "Author of life" who was killed is the same "living one [who has] risen", the divine person of the Son of God necessarily continued to possess his human soul and body, separated from each other by death:

By the fact that at Christ's death his soul was separated from his flesh, his one person is not itself divided into two persons; for the human body and soul of Christ have existed in the same way from the beginning of his earthly existence, in the divine person of the Word; and in death, although separated from each other, both remained with one and the same person of the Word.