To be alive to God, one has to be dead to the world. This is a basic principle of the spiritual life. The less one is dead to the world, the less that person is alive to God.
One of the effects of Original Sin is disordered passions. We have an inclination to love creation in place of the Creator. But to allow the goodness and beauty of the world to move us beyond itself to the absolute goodness and beauty of God is to die to the world. It is very much like dying to the stages of life: there's no entering into childhood without a dying to infancy, and there is no entering into adolescence without a dying to childhood and its pleasures, and there is no adulthood without a dying to adolescence with all its illusions and fantasies. Similarly, one cannot be alive to God without dying to the world.
In today's gospel, James and John were not, at this point in their lives, dead to the world, and despite having spent time with Jesus, they were not alive to God. They were ambitious. The apostles did not understand the mission of Christ the Messiah, which is why Jesus had to foretell his Passion three times. They were expecting a Messiah who would conquer, like David, a warrior king, who would overthrow the Roman Empire and re-establish the kingdom of Israel in all its dynastic glory. And they wanted a place at Jesus' left and right hand, a place of high honor. They were not thinking as Christ thinks, but as man thinks. We see this even in Peter, immediately after Jesus gave him the authority of the keys of the kingdom. We read:
From that time on, Jesus began to show his disciples that he must go to Jerusalem and suffer greatly from the elders, the chief priests, and the scribes, and be killed and on the third day be raised. Then Peter took him aside and began to rebuke him, "God forbid, Lord! No such thing shall ever happen to you." He turned and said to Peter, "Get behind me, Satan! You are an obstacle to me. You are thinking not as God does, but as human beings do."
The human heart is inordinately ambitious, it seeks to preserve itself at all costs, and left to itself, it loves itself more than anyone else and encourages others to do likewise. It seeks its own honor and glory, and it can do all this in the presence of the Person of Christ without shame. Not even the mother of James and John was seeking the honor of Christ their king, only her own honor, through her sons.
What is particularly interesting is that when this gospel was actually written, James was already a martyr; he already drank from the cup of suffering that Jesus spoke of in this gospel. So there is a reason why the writer of the gospel of Mark chose to preserve the memory of this shameful event in the life of James and John. It's a perennial temptation for all those called to serve Christ, in particular those called to be Apostles. Jesus addressed this when he criticized the scribes and Pharisees, who "love places of honor at banquets, seats of honor in synagogues, greetings in marketplaces, and to be addressed as 'Teacher'" (Mt 23, 6). Jesus explicitly exhorts us to seek the lowest place (Lk 14, 10). It is not up to us to raise ourselves up, nor even to elevate others; it is the Lord who will do so. I'm convinced that Karl Rahner, one of the greatest theologians of the 20th century, was right when he said that the greatest glories of the Church remain unknown and will only be known in eternity. There are many among us who have suffered tremendous adversity and endured through it with the greatest faith; they are completely hidden from the world and from the eyes of the visible Church. Water is the most powerful force in nature, and yet water always seeks the lowest place.
But there are still people in this world, in the Church even, who insist on vying for the highest places of honor. What they forget is that Christ, the suffering servant of Isaiah, brought about a great reversal; the highest place is now the lowest place, and the lowest place is really the highest. The cross is the throne that Christ chose for himself, thorns his crown, and 'Christ crucified' is the identity he wanted for himself. Poverty, eating with tax collectors and sinners, choosing to become ritually unclean by associating with the sick and the forsaken, touching them, healing them, all of which was repugnant to the religious leaders of the time, this is what he chose for himself; unintelligible to those who have not died to the world.
And yet James and John and all the Apostles eventually came to understand. So what was it that changed them? It was the fact that they were plunged into suffering and darkness as a result of the arrest of Jesus, his trial, and his death sentence, which in their minds was proof positive that everything Jesus said and stood for was a failure. He could not have been the Messiah, the Christ, because he did not defeat the Romans, rather, the Romans defeated him, apparently so. That darkness and utter despair was a genuine experience of death for them. What happened next? He rose from the dead, he appeared to them, and on Pentecost the Holy Spirit descended upon them, giving them the fullness of the divine life, completing their death to the world, which is why they now had a courage that was unrecognizable, as we see in the Acts of the Apostles. They were entirely unconcerned about their own livelihood, unconcerned about their own lives. They were ready for martyrdom, and it was their blood and the blood of countless Christian martyrs in the first three centuries of the Church that was the seed from which sprang the life of the Church.