Jonas, through the memories transmitted to him by the Giver, experiences all kinds of sights and sounds and emotions that have been made unavailable to the other members of the community because of its decision to pursue "sameness" in all possible aspects of life. Jonas struggles often with what he perceives as the unfairness of this situation, wishing that others could experience some of the new things he is encountering.
When Jonas discovers that breaking the rules and transmitting pleasant memories to Gabe helps the baby sleep peacefully, he begins to consider more deeply how it might be possible to share some of his new discoveries with others in the community. This involvement of persons besides the Giver and the Receiver in recognizing and feeling such experiences is revolutionary and possibly threatening to the community, but Jonas still finds himself thinking about it more and more.
Things could change, Gabe. Things could be different. I don't know how, but there must be some way for things to be different. There could be colors. And grandparents. And everybody would have memories. You know about memories.
Jonas acquires wisdom and compassion through his exposure to these positive memories.
The change caused in Jonas is not so much from the positive memories of the mountains, but from the experience of pain that preceded them. The Giver tries to balance the pain with positive memories. This leads Jonas to realize how different he is from the rest of his community.
They have never known pain, he thought. The realization made him feel desperately lonely, and he rubbed his throbbing leg. (p. 110)
Jonas grows as a person as he begins to develop wisdom, one of the traits that the Elders said he would gain through his training. Jonas also begins to develop empathy, a trait pretty much missing from his community. It is through this empathy that he begins to transmit memories, including the memory of ocean, to soothe Gabe.
He wondered, though, if he should confess to The Giver that he had given a memory away. He was not yet qualified to be a Giver himself; nor had Gabriel been selected to be a Receiver. (p. 117)
Jonas also grows when he passes on the memory because he realizes that he has a power he never knew he had. With this power comes the responsibility to help others, now that Jonas also has empathy, or compassion.
He saw all of the light and color and history it contained and carried in its slow-moving water; and he knew that there was an Elsewhere from which it came, and an Elsewhere to which it was going. (p. 131)
Jonas now recognizes that there is a world outside the community. He sees that he has a strength the others do not have, and he seeks to pass both the knowledge and that strength on to them. In order to do that, he leaves for Elsewhere in order to rescue himself, Gabe, and his people from a life of Sameness.
Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book). Houghton Mifflin Harcourt. Kindle Edition.