In interpreting these lines, it's important to bear in mind exactly what the Fourth Tempter is trying to do. All the Tempters are showing <PERSON> a false path -- a path that will lead to damnation. Their temptations grow progressively more subtle, until the Fourth Tempter arrives. Remember that when the Fourth Tempter first appears, <PERSON> is surprised:
Who are you? I expected Three visitors, not four.
The Fourth Tempter thus represents a temptation that comes from very deep inside <PERSON>'s own mind, deep enough that he has never confronted the possibility the <PERSON> represents. The <PERSON> points out that <PERSON> has considered the glory of martyrdom before ("You have thought of that too"). But he hasn't allowed the thought to become conscious. Perhaps for a long time it wasn't relevant, but now that it's becoming a real possibility, he's actively resisting it. Once he has the thought, it becomes possible for him to seek martyrdom for selfish reasons -- for the sake of lasting personal glory. To be martyred because the alternative was to betray God is one thing; to be martyred because you like the idea of being a saint... Well, as <PERSON> puts it himself:
The last temptation is the greatest treason; To do the right deed for the wrong reason.
It's vital to look at the immediate context, too. <PERSON> has just said to the Tempter:
Can I neither act nor suffer Without perdition?
The previous tempters wanted <PERSON> to do something: to act. 674
The Fourth Tempter wants <PERSON> to endure something: to suffer. <PERSON> is dismayed, because he had thought that by not taking action he could avoid damnation. But in this speech, the Fourth Tempter points out that there isn't really a definitive difference between acting and suffering. The actor (the one who acts) must also be a patient (one who suffers). And the same applies in reverse. In effect, the Fourth Tempter is trying to convince <PERSON> that there is no way to avoid responsibility -- quite literally, that <PERSON> is damned if he does and damned if he doesn't. And if it is, in fact, impossible to avoid damnation, <PERSON> might as well go down in a blaze of glory, and seek martyrdom for the sake of later sanctification.
But finally, it's important to recognise that <PERSON> isn't trying to present the Fourth Tempter as being fundamentally right. All the Tempters are to some degree reasonable, all of them have something genuinely tempting to offer. But their view of the world is skewed and incomplete, and <PERSON> ultimately manages to resist all of them. His final speech in Part 1 includes the line
I shall no longer act or suffer, to the sword's end.
In other words, the <PERSON> may be right to suggest there's no bright line separating suffering from acting, but he's also wrong to imply that that leaves <PERSON> with no way out. I don't fully understand what <PERSON> means when he has <PERSON> say he will "no longer act or suffer" -- it's not as if <PERSON> dies or goes into a coma at that moment -- and I would tentatively suggest that what <PERSON> has in mind is something like perfect submission to God's will and complete acceptance of whatever comes next. In his sermon, later in the play, he says "A martyrdom is always the design of God." This suggests, to me at least, that <PERSON> can see his martyrdom coming and is accepting of it -- but is also willing to let it pass by, if it's not God's will. 674