One purpose for making Swift was because Objective C is dynamic, and they thought they could get a speed boost by going fully static. The other is because they were having a hard time evolving a C-based language because C is full of plot holes. Swift is meant to be efficient but still allow abstractions, which C is really bad at. (The best you can get with C is leaky abstractions.)

This should be dynamic, but it shouldn't be LUA. It should be something like JSON. Although Lua is sandboxed, so it's safer that way, it is still an easier and bigger attack vector for hackers than JSON would be.