He's introducing the reader to a mode of vision different from the vision typically permitted him from within the poem's more or less straightforward, linear, narrative boundaries.

他在向读者介绍一种不同于这首诗里,直白的线状叙述的界限,或多或少已经容许他，显露出的设想有所不同的先见之明。

耶鲁公开课 - 弥尔顿课程节选