Final answer:
Henry uses allusion to explain the harm of remaining.
Step-by-step explanation:
Henry uses allusion in the sentence to develop his claim by explaining how it is easier to remain, but it will harm the colonist in the end.
The allusion to the song of the siren in Greek mythology warns the colonists of the danger of succumbing to temptation and choosing not to fight for their freedom.
By comparing the siren's song to shutting one's eyes against a painful truth, Henry emphasizes the need for the colonists to face the truth and take action.