Mainly, I think we can learn that Jonas is someone who cares a great deal about what is right. We also know that he wants what is truly best for his community. Finally, I think that Jonas believes strongly in the importance of people being human -- of them not giving in to the Sameness that the community has imposed on everyone.
All of these three things go together. Jonas believes that it is truly right for the people of the community to stop trying to be the same and start being more human.
From Jonas' inner thoughts we learn that he has begun to experience adolescent feelings of sexual arousal and love. He has to take the pills because of the feelings that have begun to stir inside him. We learn that the lessons and memories that have been shared by the Giver are weighing heavily on Jonas.
When Jonas learns about the feeling of love he begins to contemplate he level of feelings that people in his society have, and he comes to realize they have never really felt love or hate. Through Jonas' thoughts the reader understands that the playing the game of war can feel as destructive as the real thing if one equates it to the real event.
One of the greatest realizations about Jonas is that he had learned what death means and he has taken his memories and used them to formulate new ideas of his own needs and strengths. A good example is that he decides to share memories with Gabriel and that he takes Gabriel with him when he escapes.