The passage ahead of this is implying, by showing how the cats react to the cruelty of humans, that the cats take on the traits of their human masters. Miss Blanche, who lives with the military man, suggests making war on the humans:
Miss Blanche, having given through her tears a complete account of this event, assured me that, to maintain our own parental love and to enjoy our beautiful family life, we, the cat-race, must engage in total war upon all humans. We have no choice but to exterminate them.
Natsume, Soseki. I Am A Cat (p. 6). Kindle Edition.
The tomcat, who lives with a lawyer, is offended by the violation of property law:
And the three-colored tomcat living next door is especially indignant that human beings do not understand the nature of proprietary rights. Among our kind it is taken for granted that he who first finds something, be it the head of a dried sardine or a gray mullet’s navel, acquires thereby the right to eat it. And if this rule be flouted, one may well resort to violence. But human beings do not seem to understand the rights of property. Every time we come on something good to eat, invariably they descend and take it from us.
Ibid, pp. 6-7
Since our narrator lives with a teacher, he reacts to this situation like a teacher would: he decides that the best course of action is to wait patiently for the humans to fall and for a Day of the Cats to arrive, instead of taking proactive action like a war to bring it about.
This being a teacher's reaction is somewhat cultural, but even in English we have sayings like "Those who can't do, teach" that cast teachers as indecisive and passive. And our narrator's master definitely conforms: as we discover, he's indolent, unsociable, and a bit of a hypochondriac. He fancies himself some kind of intellectual, but as we discover later on, he buys books that he never reads, his understanding of English is tenuous at best, and he's not much of a writer. Our narrator tells us as much:
First you must understand that this master of mine lacks the talent to be more than average at anything at all; but nonetheless he can’t refrain from trying his hand at everything and anything. He’s always writing haiku and submitting them to Cuckoo; he sends off new-style poetry to Morning Star; he has a shot at English prose peppered with gross mistakes; he develops a passion for archery; he takes lessons in chanting No play-texts; and sometimes he devotes himself to making hideous noises with a violin. But I am sorry to say that none of these activities has led to anything whatsoever.
Ibid, pp. 6-7
If someone like this were living under the kind of oppression that the cats are, it's doubtful he would be at the forefront of an armed rebellion against the oppressors. The particular reason our narrator gives also sounds like something his master might say in a similar situation:
I feel that life is not unreasonable so long as one can scrape along from day to day. For surely even human beings will not flourish forever. I think it best to wait in patience for the Day of the Cats.
Ibid, p. 7
Not one paragraph ago, our narrator said he found the idea of armed war against humans a reasonable suggestion, but now he claims that life under human oppression is not unreasonable. The particular justification he gives, that "surely even human beings will not flourish forever", sounds a bit Buddhist or possibly Stoic. It's the sort of thing that someone who fancies himself an intellectual, like our narrator's master, would say to justify his own inaction, under the guise of some deeper philosophy.