What Keeps Stuff Out of the Material Plane?

[Dralnu]

What's stopping deities and demons / celestials from romping around the Material Plane and smashing / fixing things as they see fit? Usually these powerful beings ask mortals to do stuff for them but I'm not sure why in terms of roleplay.

Is there a specific book source that I should look up?

[Parra]

What's stopping deities and demons / celestials from romping around the Material Plane and smashing / fixing things as they see fit? Usually these powerful beings ask mortals to do stuff for them but I'm not sure why in terms of roleplay.

Is there a specific book source that I should look up?

Generally speaking Deities keep other Deities out

Things like demons/devils/angels/etc generally need to be summoned in as they are traditionally unable to enter the Material Plane

[TheThan]

the material Plane is quite boring and none of the cool people hang out there.

[Morquard]

I heard somewhere once that gods become vulnerable and mortal when they enter the material plane. That's a pretty good incentive for immortal being to stay as far away as they can :)

I'm not sure if that's official or also just a guess or from somewhere else though.

[WarKitty]

I've seen it fluffed as some sort of ancient contract bound by a supremely powerful artifact. Which is also really good quest material...

[darkpuppy]

It actually varies from setting to setting, and, even in the basic DnD setting, from plane to plane. For example, Fire elementals hate coming to the material plane, because it's just too darned cold!

Other reasons include a lack of interest or knowledge of the Material Plane (The Planes of Order, for example, don't actually care about the Material Plane unless they're forcibly or accidentally transported somehow, because, quite frankly, their own plane is perfect to them), deific/infernal contracts/truces (The Material Plane is acknowledged as the source of souls for the Blood War, but it's commonly acknowledged that the soul-stealing part is more of a Cold War situation... neither side wants to be too open about it, because then the other side could be, and they might get more souls...), ancient protective magics (as with Eberron and Faerun).. the list goes on. But by damn, removing the barriers is one heck of a campaign finisher! XD

[Techsmart]

In the end, to my knowledge, it is up to the DM to justify why gods are not present within the material plane for long periods of time (see the Deities and demigods book for sourcing info).
Some concepts can include:
an agreement between gods to not interfere with mortals (since mortals are a source of power for all deities).
The gods are busy enough with their own problems to worry about being next to you at all times (such as how the 9 layers of hell are constantly at battle with the infinite layers of the abyss, which keeps demons and devils constantly putting their resources - including spells - on a prioritized list).
The gods see themselves too powerful to be present on a plane, essentially destroying it and everything on it (including followers) almost immediately.
Something bars the gods from interacting - An example would be the limitations of the physical plane strictly limiting their presence, or forcing them to take the form of a mortal, threatening them to become weaker if slain in their mortal coil.
It could cause over dependence on a good god, or deter worshipers of an evil god.
To my knowledge, though, there is not one exact reason.

[Morithias]

I've often seen it explained that in terms of things like the gods well...they can't actually alter the plane short of giving spells to clerics.

That miracle spell? That isn't actually your deity helping you because you cast it. They're more helping you cause that spell actually temporarily unsealed the deity's power so it could alter the plane over a VERY small area.

[HamHam]

What's stopping deities and demons / celestials from romping around the Material Plane and smashing / fixing things as they see fit? Usually these powerful beings ask mortals to do stuff for them but I'm not sure why in terms of roleplay.

Is there a specific book source that I should look up?

Demons and Devils generally do not get Planeshift. And portals directly from the Lower Planes to the Material are rare.

Gods... presumably there's a bit of a cold war there. Also, they are kind of busy running their afterlives and directing their many champions and servants.

[Ormur]

I mostly use the standard cosmology but in my setting the gods are using the material plane as a sort of philosophical experiment, seeing how the societies of mortals evolve and what philosophies and beliefs come out ahead. Because of that it's mostly neutral territory and divine or extra-planar intervention is frowned upon except through the established channels of spells, especially divine, and at the behest of the denizens of the material plane.

Of course it doesn't preclude rules bending, subtle influences and even flagrant violations as the plot demands.

[Soren Hero]

personally, I like Yu Yu Hakusho's "Makai Barrier" and I transpose it for use in my D&D campaigns...for those who haven't seen the show, the idea is that there is a barrier between the demon world and the human world...the barrier is strong enough to repel the higher levels of demons, the S and A class demons, who individually are powerful enough to destroy the world, and the B and C demons, who are much weaker than the upper levels, but still strong enough to pose a threat to humanity...it only lets the D and E class demons through, and these demons are the weakest.

so, in my campaigns, this means that demons and devils are rare in the world...there might be a few dretches or lemures, maybe an imp or two...it makes higher level demons and devils major threats, because they are very rare, and they know it...a devil who manages to make it into the mortal world can cause a lot of problems...for example, a pit fiend can use its wish ability to cast greater planar binding and get more devils into the world...

The barrier itself provides great story arcs, i gotta tell you...stopping an evil wizard from creating a gate to the nine hells or the abyss is serious business...stopping the barrier from being destroyed is something that might band the entire world together, or create a super secret policing organization...

[Gan The Grey]

The way I see it, the Prime Material plane is unique out of all the planes. On all the other planes, souls can directly interact with the divine landscape, but on the Prime Material, all souls require some sort of vessel in order to have any sort of influence. People from the Prime can go to the other planes and interact without a problem, but it doesn't work vice versa. Spells that allow outsiders to cross planar boundaries also build them a vessel; this part of the spell is not required when those from the Prime cast it. Therefore, the same spell is much more difficult for outsiders to cast.