These three apostles represent the church. They were in what I term the "circle of privilege". In the gospel accounts, they were the only apostles present with the Lord on three significant occasions: the raising of Jairus' daughter, the Lord's transfiguration and the Lord's agony at Gethsemane.

They witnessed the Lord's
* Greatness - in the raising of the damsel
* Glory - in His transfiguration
* Grief - in His agony before the cross

Peter - The Messenger, the porter of his discourse (using the keys of the kingdom)
James - The Martyr, the pioneer in his death
John - The Minister, the pattern of his doctrine