Milton is alerting us to the significance of the word "first" in the very first line, in this wonderful act of violating the laws of iambic pentameter.

弥尔顿在第一句就促使我们注意到“,“初/先“一词的重要性,不惜违背了抑扬格五音步诗的格律。

耶鲁公开课 - 弥尔顿课程节选