The Litany is apparently a guide to a magical ritual that can seal portals. It is unclear if the ritual requires the sacrifice of one's soul or life, given that two perished to seal the portal. The Litany would be over 4,500 years old at least.
It is possible that the Litany is located at an ancient Taldan outpost that is near the ancient Dwarven stronghold of Catsbane, near the Iobarian border to the north of Varn's territory. The Taldan outpost, Bordersmark, was the center of the Second Taldan Army of Exploration's activities in this region.