jade > {A worn-out horse; hence: an opprobrious term for a woman, and often also applied to Fortune, Nature, etc. personified}
3 His chiefest lets and authors of his harms,
lets > hindrances
4 And them perforce withheld with threatened blade,
perforce > forcibly
5 Lest his lord they should behind invade;
behind invade > [attack from behind]
6 The whiles the prince, pricked with reproachful shame,
The whiles > Meanwhile
7 As one awoken out of long slumbering shade,