Asgore won't seal the barrier, even if he wanted to he is too scared.

He may be The King, but he also is afraid, you know?
There is some group of monsters who don't want the barrier to be sealed.

They are scared of another war.. or they just want to live without any distractions? I heard humans have more rules and things not to break that we do around here.
Anyways, since Asgore won't do it, we don't really need your soul.
I can make big speeches all I want, but it won't change the truth.
I now realise that trying to kill you.. was not right.

From now on..

I will become a hero some monsters takes me as!
I'll try not to kill dumbasses like you.
But I won't stumble upon to kill any human who dares hurt even one of us.

What meets them can be called karma, although I don't give karma.

I will show justice!

...

Anyways, what kind of an idiot would fall into a huge mountain?

Did you watch anime and thought you will find something there?
Hehe, me too. But I didn't climb a mountain for it.