There are some who would claim that Emrys is the greatest magic user ever to be born. They would be wrong. While he is the strongest wielder, he is not the greatest user. How can you be a user of something that runs in your veins alongside your blood? You don't; you can only wield it.
The magic is as much a part of him as a foot, or hand, or heart is for us. It works with him and for him because it is him. We are made up of parts, and we are more than their sum. The man is worth more than the worth of his magic, his heart, his head, because he is the sum of all three and more. The magic chooses the man, and it chose him: Emrys.
Emrys defends the King and his fabled kingdom because he can see what most can't. He can see behind the privilege, and the temper, and the prejudice to what lies beneath. He can see the courageous and generous heart, the open mind, and the capacity to learn and change. He defends the Once and Future King because he is the King's friend. The magic in his veins is at the King's command, and belongs to him as much as it does to Emrys, because it is for the King that the magic chose him.
There are some who would wrench that friendship – that brotherhood – apart due to their own shortsighted vision of justice. Those are the ones who would send the vision of Albion into ruins. Who are they to get in the way of Fate? Who are they to deny the prophecies of old? Who are they who would dare threaten the King when Emrys stands by his side? Those who dare are fools; the future always corrects itself, and they may very well be the casualties the correction costs.
The prophesized warlock himself doesn't know the true extent of his abilities. Why would he? He discovers new talents as he needs them. The magic he wields is instinctive, not needing words or (often) practice to obey his every whim. It is a part of him; it will do as he wishes.
The creatures of the land sense who he is, and what his veins contain. The magical ones are especially drawn to his aura of power, bringing species out of the dark who have not seen the light in decades. The very land itself thrums with his every breath, felt by none but a select few.
Emrys is a creature of magic himself, brought into being by Nature's will. It welcomes him, and keeps him safe. It made sure he had a guide, the dragon, and made sure to give him a variety of help along the way. Neither the dragon or the other advisers recognize that Nature led them to where they were to help her child. They believe they act of their own accord. They are fools, for Nature and Fate are two sides of the same coin, needing the other to work and to be complete.
The journey of the heralded warlock will be difficult, but he will never be alone. Powers far greater than magic and men have made sure of that. He will face trials and difficulties, but Emrys is a man who will be capable of handling it. After all, hasn't he already proven that? Magic does exactly what it means, never anything else. Magic chose the man, and the man chose the King. The King will choose the people when the time comes; there can be no other outcome. After all, magic makes no mistakes.