Here Jesus prophesied of his Passion to the twelve disciples for the third time. He would be betrayed by the Jewish authorities, who would condemn him to death by handing him over to the foreigners, the Romans. In their hands, he would suffer mocking, scourging and crucifixion. Jesus was telling the disciples in plain words that he would suffer and die on the cross, and, on the third day, he would be raised to life in God's Glory. He referred to his Passion as 'the cup' he was about to drink (v. 22) (or the baptism he was baptised in, cf. Mark 10:38).
Like the Zebedee brothers and others, we may not understand what 'the cup' means. We are not even curious enough to ask Jesus, 'What do you mean, Lord?' or, 'Does it have to be like what you've said, Lord?'... These are questions about the Mystery of the Cross!
Now we have seen Jesus offer himself freely to be the Lamb of God for the love of the world and everything and every person in it. (The 'Lamb of God' itself a Mystery to many people, myself included.) And thanks to the Zebedee brothers and their mother, Jesus explains to us that in God's Glory, we are to serve, not dominate, the world and everything and every person in it.
Jesus' Cross is Love and Service. When we contemplate the Cross, we contemplate the service of love.
To love and to serve in all things! Amen! May God be blessed!