Hereof > Of this unweeting > ignorant
2 And, lying down upon the sandy grail,
grail > gravel
3 Drank of the stream, as clear as crystal glass; 4 Eftsoons his manly forces began to fail,
Eftsoons > Thereupon, forthwith manly > {Pertaining to human beings; also: manly, in the modern sense}
5 And mighty strong was turned to feeble frail. 6 His changed powers at first themselves not felt,
not > [were not]
7 Till curdled cold his courage can assail,
can > did
8 And cheerful blood in faintness chill did melt,