Obviously, that provision is the “knowing the elector personally” provision. The effect of this would be that the official opposition would be satisfied to leave that in if it were a normative standard that can't be enforced through prosecution.
It's important for everybody to know that this is not a barren legal beast. The law has lots of examples where norms are enforced in different ways. It doesn't make them less legal and legally binding.
In fact, any oath system tends to be like that. It relies ultimately on the honour of the person swearing because it is so rare that somebody actually is prosecuted for breaching oaths.
This one is just making it super clear so as to prevent this disincentive for people to even vouch because they worry that they leave themselves open to jeopardy because of how subjective and abstract the idea is of knowing the elector personally. I probably don't have to explain any more. That's what it's trying to do.