I think I understand the model of reality Housepets has

[Bellatrix]

Either that or I'm completely bonkers.

Heaven is supposed to be somewhere that people can be eternally happy and content, presumably without "cheating" like directly modifying the relevant thought patterns or filling it with beings that don't suffer from usual human psychological needs.
So, if you were tasked with designing heaven and couldn't cheat, how would you do it?

This isn't an entirely unrealistic scenario by the way, dismantling the stars of a billion galaxies to feed black holes which power a supercomputer that might require mere gigawatts to house trillions of people would allow you to make a potential utopia that'd outlive the stars as the stars outlive a tau lepton.

Real-world engineering aside though, you do have to figure out how to eternally sate beings that can become numb to luxury, bored of safety and a lack of challenges, tired of the things they enjoy, lose their sense of wonder, and want to keep developing as a person and finding new talents even though that poses issues for an immortal angel.
Clearly, the biggest problem is immortality: If you say life is only adequately enjoyable up to a specific age, then an immortal being is only younger than that for an infinitesimal portion of their life if that age is a finite number. Even if that age is 10,000 years, it's an infinitesimal portion of their life.
But there's a second problem, the whole "numb to luxury, bored of safety and a lack of challenges" thing. That's not a problem with immortality, that's a problem with heaven.

So, there's two problems, the immortality problem and the luxury problem.
The luxury problem has the more obvious solution: If the issue is with heaven, then you can have mortal realms that angels can visit and be a part of.
The immortality problem is trickier though. Basically, you don't want angels with an eternity of memories, but solving that by simply getting rid of memories as necessary isn't exactly keeping them alive forever. You could perhaps make their existence not a linear experience, but instead a tangle of threads of existence that split and merge.
If you're in a dream, you don't necessarily remember your life before, even though you're the same person as outside the dream; and when you wake up, the you who was in the dream still exists. Likewise, you could have an angel's existence composed of endless mortal lives, people who are definitely that angel yet don't know it. In fact, all mortals (and even young angels) could simply be part of the existence of an older being in this reality, and those older beings might not feel infinitely old given that they may have been a mortal recently from their perspective. Or the older being may actually have been around for a finite time, because they're just a thread of a yet-older being.

This is the best model for heaven I can come up with, and it resembles... Housepets?
Supposedly, Fox is just one thread of the soul of an angel, and the way things are explained hints that all mortals are like this.
And the mortal realms aren't treated as some garbage place people spend a brief moment before they die and go to heaven forever (like in Narnia), they're treated as a valued part of existence that are also meant to be a positive experience. Angels can visit Earth and even reincarnate, plus there's no evidence of true suffering in the mortal realms. In fact, Keene drowned, and was spared from the experience then allowed to continue with his mortal life. Sure, later on for unrelated reasons he ended up in hell which could be considered mortal given that it simply exists as flair for the mortal realms, but that was more formative than suffering.

So I think Housepets is an attempt at designing a perfect model of reality for creatures with humanlike mentalities. There's endless ways it could be optimised and made more confusing, if you were some kind of godlike being who was responsible for and extremely good at this kind of thing, but it's certainly a start, and the best I've seen in any story.

[Harry Johnathan]

Intelligent observation. Being a teenage boy, however, I'm not really the best person to talk about these kinds of things, so I won't give my thoughts.

[Amazee Dayzee]

I'm only about 2 years off from being 30 and I WOULDN'T be able to understand it even if somebody broke it down really simply and slow for me to understand so I hear you.

[NHWestoN]

Sure, why not?