The speaker of “To His Mistress Going to Bed” is full of passion and desire, so it makes a certain kind of sense that the poem doesn’t follow a lot of rules—and the rules it does have, it follows sporadically. The speaker’s desire is so powerful that it overflows poetic customs. Much the same is true of the poem’s use of end-stop and enjambment: the speaker uses both frequently, but he doesn’t follow any pattern or plan. Instead, he follows the whims of his passion, using end-stop and enjambment where his desire indicates that he should.
For example, the speaker uses end-stop in both of the poem’s first two lines:
Come, Madam, come, all rest my powers defy,
Until I labour, I in labour lie.
These lines are definite, unequivocal, strong. The speaker doesn’t admit any doubt: there’s no suggestion that the mistress might talk him down. Instead, she has to pay attention to his demands—now. The use of end-stop thus helps communicate the force and power of the speaker’s desire.
Elsewhere, the speaker uses end-stop to underline his argument. For instance, take a look at the end-stops in lines 9 and 10:
Unlace yourself, for that harmonious chime,
Tells me from you, that now it is bed time.
The speaker is making an—apparently—simple point: he hears a clock chiming, so he knows it’s time to go to bed. But the “harmonious chime” is a symbol for time itself. It serves as a reminder that time is passing, that speaker and mistress are both mortal, and that they should therefore enjoy sexual pleasure while they still can. This simple detail carries a great deal of rhetorical force. And the end-stop at the end of line 10 reinforces it. It is sharp, definite—like death itself. It conveys the underlying seriousness of the speaker’s argument: that he and his mistress shouldn’t waste any time, because death is coming for them.
The speaker’s irregular use of end-stop is thus often full of meaning: when it appears, it helps him underline the force of his desire; similarly, it reinforces his arguments for why his mistress should sleep with him.