This question refers to the way in which Jonas is presented and how he compares to Asher, one of his best friends. Although their responses to language differ, the goal of the education of children in this dystopian community is to instil within them the "precision of language," and this is something that explains the care that Jonas takes with the words that he uses, as the following quote demonstrates:
Jonas was careful about language. Not like his friend, Asher, who talked too fast and mixed things up, scrambling words and phrases until they were barely recognizable and often very funny.
This quote comes from the first chapter and it is important to note how Lowry is carefully setting up the character of Jonas even before he becomes the Receiver of Memories for his community. He is described as a thoughtful, reflective individual who is very careful to describe accurately what he feels and what he is experiencing. The way that Asher is used as a foil emphasises this aspect of the character of Jonas. Note too that this is also something that gives Jonas considerable difficulty when he confronts memories that he has no experience of, such as love and war, as he is unable and unsure of how to describe them. Jonas was therefore so careful about his use of language because of the high importance his community placed on the precision of language and being able to accurately talk about emotions and feelings. It also highlights his reflective character and the way that this community was built around defining and therefore controlling every human emotion.