Von Balthasar starts by describing that Satan is not of blood and flesh, and that is more than Man, and that is against God and so he attacks us. We can only defeat him through the power of God. He says that those who reject the fire of God’s love will experience the fire in a consuming way, which is in hell.
He then continues his argument about salvation and condemnation talking about God’s attributes of mercy and justice. He exposes his argument based on the Fathers and other theologians, saying that both attributes are not mutually opposed and that one is not found without the other. He continues following Aquina’s exposition that God is just if He punishes the evildoers and He is also just when he forgives them for being just and corresponding to His goodness.
His conclusion is that Justice is subordinated to Divine Mercy; because man and everything that exists could not exist if it weren't for his Mercy, not his justice. Thus, justice is seen as a mode of God’s goodness. In other words, the work of justice is grounded in the work of mercy. Mercy is the root of all of God’s works, and because first causes persist more strongly than the effects themselves, then the conclusion is that God gives more of his goodness than what is demanded from his justice.
Joseph Pieper: Supernatural hope is man's appropriate, existential answer to the fact that these qualities in God, which to the creature appear to be contradictory, are identical.
In the second part of his argument he continues to defend his belief, against the Church Dogman that there is hell and that there are men in there. He says that he would first need to have real confirmation that hell is full. He challenges in other word, the separability of justice and mercy because of the argument he presented already about mercy being the root of justice. Ultimately he says that it is not God who condemns (due to his mercy) but it is men who continually reject Him.
Von Balthasar, Hans Urs. Dare We Hope "That All Men Be Saved: With A Short Discourse of Hell. Translated by Dr. David Kipp and Rev. Lothar Krauth. San Francisco, CA: Ignatius Press, 1988.