5 To these sprites to bring to perfect end. 6 During which work the Lady of the Lake 7 (Whom long he loved) for him in haste did send, 8 Who, thereby forced his workmen to forsake, 9 Them bound, till his return, their labour not to slake.
slake > abate, slacken
303.11
In the meane time through that false Ladies traine,
2 He was surprisd, and buried vnder beare,
Ne euer to his worke returnd againe:
4 Nath'lesse those feends may not their worke forbeare,
So greatly his commaundement they feare,
6 But there doe toyle and trauell day and night,
Vntill that brasen wall they vp doe reare:
8 For Merlin had in Magicke more insight,
Then euer him before or after liuing wight.
1 In the mean time, through that false lady's train,
train > treachery, deceit
2 He was surprised, and buried under bier,
surprised > captured unexpectedly, ensnared under bier > under a bier [underground, in a tomb]; or: in a sepulchre ("bier" sometimes taking this meaning by transference)
3 Nor ever to his work returned again: 4 Natheless those fiends may not their work forbear,
Natheless > Nevertheless