Why does Franz consider M. Hamel’s words about language to be like a Thunderclap?

Franz considers M. Hamel’s words about language to be like a “thunderclap” because they strike him with sudden and profound realization. The comparison underscores the shock and gravity of M. Hamel’s message regarding the importance of the French language and the cultural identity tied to it. Franz is awakened to the urgency of valuing his heritage, feeling an overwhelming sense of regret for not appreciating his lessons sooner. This metaphor captures the intensity of his emotional response, as the weight of their impending loss becomes painfully clear in that moment.