@botodopo:
No, originally this evil god / spirit or whatever was a living being with his own body.
The previous sword diety defeated that evil being who was most likely far stronger originally.
So here is my assumption:
The sword diety probably managed to defeat him while being gravely or even deadly wounded himself or so.
The evil being transferred its soul / spirit to the sword to escape death after being defeated.
With the sword diety being too heavily wounded to recover or even dead shortly after the battle there was no one with enough power to break the magic sword possessed by the evil being.
Therefore the only way to take care of it was to seal the sword.
Then once it was sealed you would obviously not risk the evil being escaping again so you would not try to destroy it anymore.
You would play it safe especially because there has been no appearance of any sword diety ever since.
(That Abel's mother is a sword diety is not known to anyone after all. Except her family everyone only knows and thinks about her being a sword princess - a profession 1 tier below sword diety.)
Also it could be that the story told after the sword diety defeated that evil being went like this: "The sword diety defeated the evil being but could not kill it.".
The fact that he was wounded in the battle and could not destroy the sword due to those wounds was probably overlooked.
So later even if a sword diety showed up they would believe he/she could not destroy the sword because of the story.
Hence they would not even try to have a sword diety (who is still fully healthy) destroy the sword but instead would keep the sword sealed away.