So have ever wondered what the in-game explanation is for whenever you or your friends log out of the world/server. Well take a look at the portal behind Jack Black/steve here. Notice the black frame and blue light emitting from It? You know what else in our world has a black frame and emits a similar type of blue light? If you guessed our TV screens and PC monitors you’d be right! Basically I believe (even if it’s not confirmed and I very well could be wrong but for now it’s my head canon) that the portal is symbolic of pretty much any screen that can play Minecraft and that our screens are literal portals into Minecraft’s surface world