One of the most important things is that Jonas learns what is meant by being released. Until this point, he thinks people just go off to elsewhere, but when he watches the video of a newborn baby being euthanized by his own father, he learns the truth. Additionally, when he notes that even his own father lies, his view of the ideal society where everything runs so efficiently and seemlessly begins to deteriorate. A third important thing involves Jonas realizing that the way of his society isn't the best way; he tells the Giver that he wants to share the memories with everyone so that everyone can learn about the evils they so conveniently have forgotten.
Fourthly, The Giver and Jonas work together to formulate a plan of escape for Jonas, that would allow him to leave, yet release the memories he had received from the Giver. Finally, Jonas learns that Gabe, the slowly developing baby that his family took in, is scheduled to be released the following morning. Because of this, he must act quickly and not according to the plan he and the Giver devised.