What is the significance of Chaya's name and her new tatooed identity?

She tells Hannah to go to sleep, calling her, of course, Chaya. Hannah looks down at the tattoo on her arm and says that she is not Chaya, but J197241. Gitl insists, “You are a name, not a number. Never forget that name, whatever they tell you here. You will always be Chaya – life – to me. You are my brother’s child. You are my blood.” (pg. 103) She allows Gitl to help her to an empty bunk and when she falls to sleep, she dreams of roast beef, sweet wine, and bitter herbs.