5 But yet I warn you, now assured sit
assured > (Derisively) in safety [in the protection of your cross]
6 And hide your head." Therewith upon his crest
Therewith > With that
7 With rigour so outrageous he smote,
rigour > violence outrageous > excessively fierce
8 That a large share it hewed out of the rest,
share > portion; piece sheared away
9 And, glancing down his shield, from blame him fairly blessed.
blame > injury fairly > actually, really [from blame it really did him bless]; completely blessed > spared, preserved