Jonas is more fully human in the traditional sense of the word than the other residents of his community, with the exception of the Giver, of course. In a sense, Jonas is an anachronism in his society because he possesses properties that have been dulled in the sensibilities of others.
Jonas possesses tenderness and sympathy for others. In the early chapters, during the family session Jonas tells his parents that he worries about Asher's Assignment in life.
Later, as he becomes the Receiver, Jonas begins to understand true human suffering, and his sympathies are greatly aroused. Certainly, after he watches a "release," Jonas is appalled at the insensitivity of such an inhumane act. This recognition is what motivates Jonas to flee his dystopian community.
Jonas is capable of deduction and sound reasoning; he has keen insight and is able to understand the significance of things. As he attains memories from the Giver and learns the truth of things, Jonas perceives how his supposedly perfect society is really limited and actually cruel in its strict regulations of thought and behavior. Having watched a Release, a shocked Jonas understands that his society has serious problems and is actually very restrictive.
After Jonas escapes from his community with Gabriel, having reached the opposite side of the river, he stops and looks backward.
The life where nothing was ever unexpected. Or inconvenient. Or unusual. The life without color, pain, or past.
Jonas rejects the life of Sameness and predictability because he realizes that it is stultifying and dehumanizing.