This is yet another card that received functional errata that destroyed its flavour, a la Flying Carpet. Originally, the idea was that your creatures were holed up in a castle and received protection as long as they remained inside. However, the errata removed the “unless they are attacking” clause, so now what you’ve got is some sort of hover-castle that flies along with the army and protects them as long as they stay inside. I’m not an opponent of functional errata, but it should stay flavourful (for example: adding the line “but remains named X” a la Sakashima the Imposter for all Clone-like cards instead of changing the legendary rule). I know it was to “make it simpler” but it wasn’t confusing in the first place! Your dude runs out and stabs a guy and if it has Vigilance, he runs back into the castle.
As for the card itself, it’s pretty “meh”. The toughness boost gives your creatures more survivability and the errata did make it a little better since attacking creatures can get the bonus as well. I don’t know if it’s worth 4 though; maybe 3 or 2 with a drawback (like not effecting attacking creatures maybe?). Not a bad card; I just wish they hadn’t changed the wording.
Pros: Toughness boost to all your untapped creatures
Cons: Errata makes no sense, costs 4