Holmes was coming upstairs. Holmes would burst open the door. Holmes would say "In a funk, eh?" Holmes would get him. But no; not Holmes, not Bradshaw...There remained only the window, the large Bloomsbury-lodging house window, the tiresome, the troublesome, and rather melodramatic business of opening the window and throwing himself out. It was their idea of tragedy, not his or Rezia's (for she was with him). Holmes and Bradshaw would like that sort of thing. (He sat on the still). But he would wait until the very last moment. He did not want to die. Life was good. The sun hot. Only human beings -- what did they want? ...Holmes was at the door. "I'll give it to you!" he cried, and flung himself vigorously, violently down on to Mrs. Filmer's area railings.What struck me most about the passage was how focused Septimus is on Bradshaw and (especially) Holmes. His whole reason for killing himself at this point seems to be that he needs to escape from their 'treatments' any way he can, even if that requires fleeing into death. As Holmes is a doctor, it's both ironic and horrible that he is causing his own patient's death by his lack of comprehension.
This whole passage also serves to drive home the idea that suicide is never definite. Up to this point, Septimus seemed to be improving significantly, and even in the moments before suicide he says that he does not want to die. If Holmes had not been so ignorant or Rezia had been able to turn him away, Septimus' death could have been avoided entirely. This idea makes Septimus' death all the more tragic and gives us insight into how we ought to deal with suicide. Suicidal impulses are often very much in the moment, and recognizing that gives us a much better chance of preventing people from taking their own lives with quick intervention and better understanding of the underlying problems.