1 Fair goddess, lay that furious fit aside,
fit > mood, humour; or: strain of music
2 Till I of wars and bloody Mars do sing,
Till > (Perhaps a reference to the mooted twelve-book work on the public virtues; see I:92-4)
3 And Briton fields with Saracen blood bedyed,
Briton > British Saracen > {Arab, Moslem; pagan; here = Spanish} bedyed > dyed on all sides, thoroughly dyed; the prefix is also an intensive, hence: soaked
4 'Twixt that great Faery Queen and paynim king,
paynim > pagan, heathen king > (Philip II of Spain)
5 That with their horror heaven and earth did ring,
ring > cause to resound (cf. line 7); or, perhaps: encircle, encompass