"It was the first time he had had anything to do." (1.88)
Forster portrays idleness in the novel as a sign of class: the higher your social status, the less actual work you have to do. Gentlemen like Philip spend their days reading books, making witty jokes, and carrying on philosophical conversations. So when Mrs. Herriton sends Philip to bring Lilia home before she makes a fool of herself, Philip feels all giddy to have something important to do.
There was no more to do in the house, and he spent whole days in the loggia leaning over the parapet or sitting astride it disconsolately.
"Oh, you idle boy!" she cried, pinching his muscles. "Go and play pallone." (3.14)
When Gino marries Lilia, he no longer has to work for a living since Lilia has enough money to support both of them. But idleness breeds discontent in this case. Beyond feeling bored out of his mind, Gino is concerned that Lilia holds all the power in their marriage. Notice how Lilia babies him by calling him a "boy," pinching him and telling him to "go and play." When Gino tries to assert his authority, that's when trouble really starts to brew.
"We've come here to get the baby back, and for nothing else. I'll not have this levity and slackness, and talk about pictures and churches." (6.59)
Harriet has one sole purpose in mind right now, and nothing is going to distract her from it. She bosses Philip around to make sure that he doesn't fall into his usual "levity and slackness." But is it better to be like Harriet, whose actions have terribly tragic consequences, or like Philip, whose passivity means that nothing ever gets done?
"That's not doing anything! You would be doing something if you kidnapped the baby, or if you went straight away. But that! To fail honourably! To come out of the thing as well as you can! Is that all you are after? […] Settle it. Settle which side you'll fight on. But don't go talking about an 'honourable failure,' which means simply not thinking and not acting at all. [...] Fight as if you think us wrong. Oh, what's the use of your fair-mindedness if you never decide for yourself?" (7.60)
Miss Abbott is totally not okay with Philip's idleness, which she reads as apathy. In her opinion, it'd be better if he had kidnapped the baby—at least Harriet can't be accused of passivity and inaction. But Miss Abbott thinks that it's a crime for someone as smart as Philip to act like a brainless puppet… and we kind of agree with her.
"It's not enough to see clearly; I'm muddle-headed and stupid, and not worth a quarter of you, but I have tried to do what seemed right at the time. And you—your brain and your insight are splendid. But when you see what's right you're too idle to do it. You told me once that we shall be judged by our intentions, not by our accomplishments. I thought it a grand remark. But we must intend to accomplish—not sit intending on a chair." (7.62)
Caroline isn't sparing Philip any of her criticism. Now she's throwing his own words back at him, arguing that having good intentions alone isn't good enough—you have to put those intentions to use by doing something. Actions speak louder than words, and while Philip can talk the talk, he doesn't walk the walk.
"You appreciate us all—see good in all of us. And all the time you are dead—dead—dead." (7.66)
Miss Abbott equates Philip's passivity with death—if he's not going to act on his words then he might as well be "dead, dead, dead." It's important to Caroline that Philip stop being a puppet doing his mother's every bidding, and never deciding things on his own. Philip seems perfectly content with his life and doesn't see any need to change. Is Philip even capable of change or is he doomed to a life of inactivity?
"Miss Abbott, don't worry over me. Some people are born not to do things. I'm one of them. [...] I never expect anything to happen now, and so I am never disappointed. […] I seem fated to pass through the world without colliding with it or moving it—and I'm sure I can't tell you whether the fate's good or evil. I don't die—I don't fall in love. And if other people die or fall in love they always do it when I'm just not there. (7.67)
We can't help feeling that the way Philip describes his life is kind of sad and verging on pathetic. Philip is happy with an uneventful existence—he expects nothing, he lets things happen to him (or not happen to him), he's never around for anything important to take place. He never seems to experience FOMO (fear of missing out), and we think he needs a serious lesson in YOLO.
"I wish something would happen to you, my dear friend; I wish something would happen to you." (7.68)
Even Miss Abbott feels sorry for Philip. It would kind of suck to go through life and have nothing happen to you, good or bad. This is Forster's warning to us that an inactive life is a wasted life.
"Every little trifle, for some reason, does seem incalculably important today, and when you say of a thing that 'nothing hangs on it,' it sounds like blasphemy. There's never any knowing—(how am I to put it?)—which of our actions, which of our idlenesses won't have things hanging on it for ever." (7.86)
If we don't know what the consequences of our actions are going to be, should that prevent us from acting? When we don't have a crystal ball that allows us to look into the future, it can be hard to know which course of action is the right one to take. But Forster seems to think that any form of action is better than sitting idly by, refusing to commit one way or another.
People had been wicked or wrong in the matter, no one save himself had been trivial. (8.2)
The matter in question here is the fate of Lilia's baby. Philip realizes that out of everyone involved in the situation (Harriet who was "wicked" for kidnapping the child; Miss Abbott who was "wrong" for trying to separate the baby from his father), he is the only one who was "trivial," or inconsequential. Because Philip fails to act, his passivity means that he has no effect, good or bad, on the events happening in his own life.
"It happened because I was cowardly and idle." (8.13)
Philip finally admits that the events leading up to the baby's death happened at least in part because he was too cowardly to act. His inaction meant that Harriet had to take charge, leading to the kidnapping (and ultimately death) of the child. Sometimes failing to do anything is even worse than doing something wrong.
"You're without passion; you look on life as a spectacle; you don't enter it; you only find it funny or beautiful." (10.57)
Miss Abbott disapproves of Philip's detachment from life, his tendency to look at life as a "spectacle," something to be watched from a distance and not participated in with passion. Is Philip someone who is even capable of feeling real passion? Or is he too emotionally disconnected from people and reality to ever full take part in it?