In the beginning, Jonas’s feelings are the same as everyone else in the community. He is instantly obedient, and has very few real problems.
Their parents, of course, were part of the ritual; they, too, told their feelings each evening. (ch 1, p. 5)
Jonas has no troubles, and neither do any of his family members, as the book begins. When Jonas begins his training, he realizes that he has been lied to all of his life. He finds out that feelings do exist, and pain is real. He begins to understand that his community has sacrificed all feelings in order to prevent bad ones.
When Jonas says, "There could be love," he is acknowledging the problems in his perfect community (ch 16, p. 129). Jonas’s parents do not understand the word. They chide him for being imprecise. Love and affection do not really exist in their life. Love is a meaningless word.
Jonas stared at them. Meaningless? He had never before felt anything as meaningful as the memory. (ch 16, p. 127)
When Jonas does come to understand his feelings, and realize that no one else has any real feelings, he takes action. He sees his father kill a defenseless newborn, and he no longer has any affection for him. He decides to leave, and return the memories to the community so that they can feel for the first time.
Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book). Houghton Mifflin Harcourt. Kindle Edition.