Even before he is chosen to be the next Giver, Jonas is sensitive to language; while he has been careful not to say the inappropriate word, he also is sensitive to his surroundings while almost everyone in the society has been desensitized and can express only superficial emotion.
Once he is selected to be a Giver, Jonas now is overwhelmed that he can use words that have been forbidden.
His mind reeled. Now, empowered to ask questions of utmost rudeness--and promised answers--he could, conceivably (though it was almost unimaginable), ask someone, some adult, his father perhaps, "Do you lie?"
As he begins his training, Jonas is enabled to feel sorrow, joy, heat and cold, pain, loss of blood, and other sensations such as sexual feelings. The Giver transmits to Jonas the feel of snow and sunshine, things that do not exist in the environment of the society where Climate Control exists. Jonas acquires the ability to see color as the apple he sees is red, and he starts to realize what has been lost. For the Giver is the one man that can remember in times when memory is needed.
Jonas's range of emotions were much deeper and more meaningful than those of his family and friends. This was due to the memories that the Giver transferred to Jonas, and he thus realises that when his family expresses that they are feeling some sort of emotion, that they never truly experienced such true emotions.