Final answer:
The purpose of the rhetorical device in these sentences is to make the main points more memorable through repetition.
Step-by-step explanation:
The purpose of the rhetorical device in these sentences is to make the main points more memorable through repetition. In each sentence, the phrase 'We must' is repeated to emphasize the importance of the actions that follow: 'learn from our mistakes', 'keep our sights on our goal', and 'persevere'. This repetition creates a strong and memorable message for the reader or listener.
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