I am a bit confused about the use of commas before and after the "as" phrase. I mean, is it possible that there is no comma before and after such a phrase? For instance, the man AS YOUR GUARDIAN will always protect you.
What you describe is a parenthetical comment. This means that the sentence makes sense if you delete this segment.
You could write it like this:
Your parents (as your guardians) will always protect you.
However this makes the sentence rather heavy on punctuation. A less distracting way to write it is to use commas instead of parentheses:
Your parents, as your guardians, will always protect you.
The commas are needed to mark out the parenthetical portion. Theoretically there could be occasions where the commas could be omitted without making the sentence ugly or confusing, but I can't think of one at the moment.