In this book von Balthasar explores the nature of Jesus Christ as the expositor of God; the only being who understands God (since he is God) and also understands man (since he is man), and so the only being who can speak both languages, in a manner of speaking. Jesus' words and actions during his mortal life were insufficient to this task; all 4 gospels make clear that even his apostles did not understand his sayings until after his death, resurrection, and ascension.
And so von Balthasar also tackles Our Lord's experience in Hell on Good Saturday; these pages being the source of much of the controvery surrounding von Balthasar. Von Balthasar takes Our Lord's words on the Cross ("My God, My God, why have you forsaken me?") in a different way, as applying to his whole being (Jesus having two natures, but a single personality, hence a single subject, so that everything Jesus experiences, he experiences fully as both man and God). Von Balthasar explores what it means for the persons of the Trinity to be absent from each other.
It is already hard enough to grasp the Trinity, so I am even more unable to grasp the idea of subsistent relationships (this being a technical term for the relationship of the persons in the Trinity to each other) being truly forsaken. As we all know, the greatest of theologians and saints go astray at times; Thomas Aquinas considered and rejected the idea of the Immaculate Conception. So even if von Balthasar is mistaken in this matter - and I am not sure either way - he remains a substantial and original thinker, full of insight, while never suggesting or encouraging or even considering the possibility of a rupture with the Church.