In Chapter 16, Jonas is recovering from receiving the knowledge of war. He is distressed by these memories, but his mental horizons are soon expanded even more when the Giver transmits his own favorite memory; of Christmas night with family and friends. He sees the various traditions -- gifts, candles, the tree -- and although he doesn't quite understand them, he feels a deep connection to the memory.
"What did you perceive?" The Giver asked.
"Warmth," Jonas replied, "and happiness. And -- let me think. Family. That it was a celebration of some sort, a holiday. And something else -- I can't quite get the word for it."
"It will come to you."
(Lowry, The Giver, Google Books)
Jonas is given the concept of Love, something that he has never considered in his life. He soon comes to the realization that he has never actually experienced familial love; his own parents take care of him because it is their role and because it pleases them, not because they love him. Jonas also realizes that while his parents don't "love" him in the way he now desires, he himself does love the infant Gabriel, with whom he shares his memories. This epiphany helps Jonas later when he discovers the true meaning of Release, and his father's role in the practice.