Skullius hadn't known what the Oath of Mourning was, or did.
The moment he sensed it, he knew that it was what he was looking for and went for it.
He didn't know that it would slow down anyone who approached it, whether they were the humblest of Sif or the most pureblood El Sif.
He also hadn't known that it hid the actual location of the thing he was looking – something that the scroll Darwel had given him back then mentioned.
A shrine.
She had said that the Luminants had a some kind of supreme being they revered. Her scroll had then revealed to Skullius that there something built by the Sif in the past. Something that represented this divine being whom he had been speculating about.
Yet Skullius' ignorance was still rewarded.