The Sons of Thunder

Jesus called James and John "the sons of thunder".

And James the son of Zebedee, and John the brother of James; and he surnamed them Boanerges, which is, The sons of thunder.
- Mark 3:17 (KJV)

But why? Is it a good thing, or is it a bad thing?

Here is what Ellen White says.

Unlikely Leaders tells the story of the Christian church's beginning. Jesus left the work in the care of eleven men who seemed, humanly speaking, to be poor choices for establishing a world-wide movement to bring a rebellious planet back to its Creator. Their number included a brash fisherman who crumpled under pressure, a young man and his brother who were so hot-headed that they earned the nickname "sons of thunder," a tax collector who had enriched himself by working for the enemy, a patriot ("Zealot") who may have belonged to a group known for assassinating enemy collaborators, and a loyal but doubt-filled man who could rarely see the bright side of anything. A little later someone else joined them who had originally done his best to destroy them. What could come of a group like this?
- Ellen White, Unlikely Leaders, p. 5

And again from Early Writings.

The confiding love and unselfish devotion manifested in the life and character of John present lessons of untold value to the Christian church. John did not naturally possess the loveliness of character that his later experience revealed. By nature he had serious defects. He was not only proud, self-assertive, and ambitious for honor, but impetuous, and resentful under injury. He and his brother were called "sons of thunder." Evil temper, the desire for revenge, the spirit of criticism, were all in the beloved disciple. But beneath all this the divine Teacher discerned the ardent, sincere, loving heart. Jesus rebuked this self-seeking, disappointed his ambitions, tested his faith. But He revealed to him that for which his soul longed - he beauty of holiness, the transforming power of love.
- Ellen White, Early Writings, p. 539/540

And again from The Desire of Ages.

All the disciples had serious faults when Jesus called them to His service. Even John, who came into closest association with the meek and lowly One, was not himself naturally meek and yielding. He and his brother were called "the sons of thunder." While they were with Jesus, any slight shown to Him aroused their indignation and combativeness. Evil temper, revenge, the spirit of criticism, were all in the beloved disciple. He was proud, and ambitious to be first in the kingdom of God. But day by day, in contrast with his own violent spirit, he beheld the tenderness and forbearance of Jesus, and heard His lessons of humility and patience. He opened his heart to the divine influence, and became not only a hearer but a doer of the Saviour's words. Self was hid in Christ. He learned to wear the yoke of Christ and to bear His burden.
- Ellen White, The Desire of Ages, p. 295/296

This, to me, shows that God can use everybody. No matter what the starting point is.