The Cross is about the vulnerability of God, it is about God placing himself into our hands.
In the Crucifixion God is scourged, spat upon, crowned with thorns, nailed to the Cross and left to die.
Upon the Cross the ultimate battle, is revealed the terrible truth of God, the all powerful becomes all weakness, Life himself submits to death, the sinlessness is overcome by sin. Fallen man who has fought with God from his beginning now enters the final battle.
Before us is set the incredible power of man, he can and does crush God, remove from existence, expel him from the earth he had created.
Before us is set the love of God, that he for love of us is willing to be defeated. For us Immortality becomes mortal.
The doctrine of Hell is essentially about freewill. Man can choose to embrace God for all eternity or to reject him, to say 'yes' or 'no', we can choose between life and death. In a very real way we are made like God himself, we are eternal.
On the Cross God shows himself powerless but we are never powerless, God removes his choice by choosing to love us. God accepts us with utter love and we are called to make a decision of accepting or rejecting him. Catholic theology never teaches God or his Grace is irresistable. In each of our acts we can either reject or accept God.
We can be in the crowd which shouts Hosanna - 'Save us' as we follow Jesus in the great sacrificial procession from misery (Bethany means 'House of Misery) to be at peace with God (Jerusalem means 'the View of Peace') or we can be in that other crowd which rejects him and shouts "Crucify him" and does crucify him.
The choice is eternal because we are eternal, we can choose God which is Heaven or Hell where the pain is our own decision to reject God.
Heaven and Hell are both a single moment but an eternal moment.