rest > {Socket in the saddle for the heel of the lance}
4 Tho when still he saw him towards pace,
Tho > Then towards > [in his direction]
5 He gan rencounter him in equal race.
gan rencounter > did engage equal race > {The level course along which the two jousting knights in a tourney charge toward one another, here used fig.}
6 They been met, both ready to affrap,
been met > [came together in battle] affrap > strike (WUFQ)
7 When suddenly that warrior gan abase
that warrior > [Guyon, as the next stanza makes clear] gan abase > did lower
8 His threatened spear, as if some new mishap 9 Had him betide, or hidden danger did entrap.