At the end of the novel, Jonas is mature and independent, but at the beginning he is obedient and entirely dependent on the community to tell him what to think.
When Jonas is worrying about the Ceremony of Twelve, he is young and immature. He describes himself as reflective, but obedient and unquestioning. He accepts things as they are.
Instantly, obediently, Jonas had dropped his bike on its side on the path behind his family's dwelling. He had run indoors and stayed there, alone. (ch 1, p. 2)
When Jonas is chosen Receiver of Memory, his life completely changes. He learns about colors, love, the past, and memories. He realizes that differences are causes for celebration, not alarm.
Jonas first notices that he is different before he even begins his training. He notices that an apple changes in mid-air. Later, at the ceremony, he sees faces change. The Giver tells him that he is beginning to see the color red.
With the memories, Jonas acquires wisdom. He learns that things could be different.
"Listen to me, Jonas. They can't help it. They know nothing."
"You said that to me once before."
"I said it because it's true. It's the way they live. It's the life that was created for them. (ch 20, p. 153)
Jonas learns not to hate his family or his people, but instead to pity them. He decides to run away, so the memories can return to the people and they can get rid of Sameness. To leave the community, especially with Gabe, requires a great deal of personal strength and maturity on Jonas’s part.
Jonas is able to protect himself and Gabe from searches, and make it safely to Elsewhere.
Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book). Houghton Mifflin Harcourt. Kindle Edition.