The difference between Ogion’s mode of teaching and that of the School of Wizardry on Roke is a dramatization of the themes of A Wizard of Earthsea. There is a sense in which Ogion stands at the end of the metaphorical road that Ged has to travel in the course of the novel, and so the disagreement between the two of them in chapter 2 prefigures the lessons that Ged is going to learn in the remainder of the story.
There are, I think, three parts to this. First, Ogion is an ascetic: he does not value material wealth or fame. Though the folk of Re Albi owe Ogion their lives and property for saving the city from the earthquake, nonetheless his standard of living remains similar to that of the neighbouring farmers and herders:
The mage’s house, though large and soundly built of timber, with hearth and chimney rather than a firepit, was like the huts of Ten Alders village: all one room, with a goatshed built onto one side. There was a kind of alcove in the west wall of the room, where Ged slept. Over his pallet was a window that looked out on the sea, but most often the shutters must be closed against the great winds that blew all winter from the west and north.
Ged, on the other hand, desires fame and the respect of his peers:
Yet other cravings were in him that would not be stilled, the wish for glory, the will to act.
but this leads him into the disastrous rivalry with Jasper.
Second, Ogion believes that power over other people is hollow and that compulsion is not true learning:
“Ged, my young falcon, you are not bound to me or to my service. You did not come to me, but I to you. You are very young to make this choice, but I cannot make it for you.”
There are several occasions where Ged’s attempts to compel others to his will leads to disaster or near-disaster. In A Wizard of Earthsea his summoning of the spirit of Elfarran on Roke Knoll leads to the release of the shadow; and his attempt to compel Pechvarry’s son to turn back from the country of the dead nearly causes his own death. In The Farthest Shore he attempts to teach the sorcerer Cob to desist from the Pelnish Lore:
“I made him go with me into the Dry Land, though he fought me with all his will and changed his shape and wept aloud when nothing else would do.”
But this backfires terribly:
“I was in Paln,” he said to Ged, “after you, in your pride, thought you had humbled me and taught me a lesson. Oh, a lesson you taught me, indeed, but not the one you meant to teach!”
Third, Ogion does not act until he understands the consequences of his actions:
“Ged, listen to me now. Have you never thought how danger must surround power as shadow does light? This sorcery is not a game we play for pleasure or for praise. Think of this: that every word, every act of our Art is said and is done either for good, or for evil. Before you speak or do you must know the price that is to pay!”
This is dramatized by Ogion’s refusal to change the weather merely for his own convenience:
For when it rained Ogion would not even say the spell that every weatherworker knows, to send the storm aside. In a land where sorcerers come thick, like Gont or the Enlades, you may see a raincloud blundering slowly from side to side and place to place as one spell shunts it on to the next, till at last it is buffeted out over the sea where it can rain in peace. But Ogion let the rain fall where it would.
By contrast, Ged is prone to thoughtless and reckless action.
So the first two-thirds of A Wizard of Earthsea consists of Ged learning the lessons that Ogion was prepared to teach him, but learning them instead in the only way he was capable of, that is, through bitter experience:
“I have walked with great wizards and have lived on the Isle of the Wise, but you are my true master, Ogion.”