surely ridicules the grandeur with which Satan's lair is previously described - seems sad and cold, rather than blazing with hellfire.

certainly we see Satan potentially presented as ridiculous, despite sitting on his 'throne of royal state', we see his 'merit rais'd', the chosen lexis of 'insatiate' suggests a restlessness in Satan, potentially portraying him as unable to take his defeat, which might ridicule his efforts entirely.

clearly presents satan as important & of status (trait of a classic epic hero, post battle?) could link to Milton's own attitudes in dispute of the monarchy - perhaps he allows Satan to sit on a throne because of this.

emphasises the significance of perception - as either heaven or hell can be perceived as one or the other, this being entirely dependant on who's looking -as evil can bask in the 'glory' of eternal damnation and suffering whilst good is drawn to god's splendour & light in heaven.

this is perhaps also unusual for the epic form, as the heroic figure tends to be confident on the lines between good and evil - yet this line almost suggests we should prepare for those lines to become unclear

connotes notions of secrecy, as hell as clandestine and shameful (it's residents have been denied the divinity & glory of heaven). in agreeance with the comments above, Dante's depiction of hell as the 'inferno' meets Milton's description of hell as not simply unidimensional, but with 'land', 'lake with liquid fire' and not expempt from the elements 'subterranean wind' (yet evidently devoid of light).