The simple answer is it reconciled justice with mercy. Apart from the cross there is no other ladder by which we may get to heaven.458
IN BRIEF
619 "Christ died for our sins in accordance with the scriptures" (I Cor 15:3).
620 Our salvation flows from God's initiative of love for us, because "he loved us and sent his Son to be the expiation for our sins" (I Jn 4:10). "God was in Christ reconciling the world to himself" (2 Cor 5:19).
621 Jesus freely offered himself for our salvation. Beforehand, during the Last Supper, he both symbolized this offering and made it really present: "This is my body which is given for you" (Lk 22:19).
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" (I 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).
IN BRIEF
619 "Christ died for our sins in accordance with the scriptures" (I Cor 15:3).
620 Our salvation flows from God's initiative of love for us, because "he loved us and sent his Son to be the expiation for our sins" (I Jn 4:10). "God was in Christ reconciling the world to himself" (2 Cor 5:19).
621 Jesus freely offered himself for our salvation. Beforehand, during the Last Supper, he both symbolized this offering and made it really present: "This is my body which is given for you" (Lk 22:19).
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" (I 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).