The gods think of the giants (called Jotuns) as 'others.' That means they're the creatures the gods think of as being completely the opposite of them, everything they're not. They feel they must protect themselves from the giants and keep them from intermingling with the gods. That's why the gods hire the "stone-mason" to build an enormous wall around Asgard. Of course, by attempting to separate themselves from their 'others,' the gods actually invite a giant into their city. Maybe there's a hidden message in there somewhere.
Another 'other' in this story, and in most stories in Norse mythology, is Loki. It's easy to forget that Loki is actually the son of two giants. So that means he's a giant, right? Well, no, not really. He hangs out with the gods and is accepted by them, so does that make him a god? Again, not really. He's neither a giant nor a god. He's in between both, which is what his ability to shape-shift symbolizes. In this story, Loki puts his shape-shifting ability to good use, and gives birth to a child that's just as in-between as he is. The child (OK, baby horse) Loki conceives with Svadilfari is only sort of a horse – how many horses do you know that have eight legs and can fly to the Underworld? Sleipnir is an 'other' just like his parent, Loki.