4 Where no living creature he mistook,
mistook > [had erroneously taken to be; hence: had supposed to be]
5 With great indignance he that sight forsook,
indignance > indignation
6 And down again himself disdainfully 7 Abjecting, the earth with his fair forehead struck;
Abjecting > Casting down ("down" in line 6 is thus tautological and intensive)
8 Which the bold virgin seeing, gan apply
Which the bold virgin seeing, gan > [Which seeing, the bold virgin did]
9 Fit medicine to his grief, and spoke thus courteously:
Fit > Appropriate