This ultimate solidarity is the final point and the goal of that first ‘descent,’ so clearly described in the Scriptures, into a ‘lower world’ which, with Augustine, can already be characterised, by way of contrast with heaven, as infernum. Thomas Aquinas will echo Augustine here. For him, the necessity whereby Christ had to go down to Hades lies not in some insufficiency of the suffering endured on the Cross but in the fact that Christ has assumed all the defectus of sinners…Now the penalty which the sin of man brought on was not only the death of the body. It was also a penalty affected the soul, for sinning was also the soul’s work, and the soul paid the price in being deprived of the vision of God. As yet unexpiated, it followed that all human beings who lived before the coming of Christ, even the holy ancestors, descended into the infernum. And so, in order to assume the entire penalty imposed upon sinners, Christ willed not only to die, but to go down, in his soul, ad infernum. As early as the Fathers of the second century, this act of sharing constituted the term and aim of the Incarnation. The ‘terrors of death’ into which Jesus himself falls are only dispelled when the Father raises him again…He insists on his own grounding principle, namely, that only what has been endured is healed and saved.
That the Redeemer is solidarity with the dead, or, better, with this death which makes of the dead, for the first time, dead human beings in all reality- this is the final consequence of the redemptive mission he has received from the Father. His being with the dead is an existence at the utmost pitch of obedience, and because the One thus obedient is the dead Christ, it constitutes the ‘obedience of a corpse’ (the phrase is Francis of Assisi’s) of a theologically unique kind. By it Christ takes the existential measure of everything that is sheerly contrary to God, of the entire object of the divine eschatological judgment, which here is grasped in that event in which it is ‘cast down’ (hormemati blethesetai, Apocalypse 18, 21; John 12; Matthew 22, 13). But at the same time, this happening gives the measure of the Father’s mission in all its amplitude: the ‘exploration’ of Hell is an event of the (economic) Trinity…This vision of chaos by the God-man has become for us the condition of our vision of Divinity. His exploration of the ultimate depths has transformed what was a prison into a way.
–Hans Urs von Balthasar (1905-1988), Mysterium Paschale: The Mystery of Easter [emphasis mine]