Final answer:
In John Milton's 'Paradise Lost' Book 10, the speaker of the line 'Inexplicable Thy justice seems...' is Satan, expressing his inability to understand divine justice.
Step-by-step explanation:
The speaker of the line "Inexplicable Thy justice seems..." is Satan, who is the central character in Book 10 of John Milton's epic poem Paradise Lost. This particular line reflects Satan's puzzlement and dismay at what he perceives as the unfair and mysterious nature of the justice meted out by God. In his speech, he grapples with the consequences of his own actions and the overarching divine justice that dictates the outcomes of those actions. The epic poem touches on many themes, but the quest for understanding divine justice is a key element that influences the characters' motivations and the unfolding of the narrative.