This sounds fringe, and it may well have been by that time. But it isn’t all that different from the 1st, 2nd, and 3rd-century Christian practices that bothered the pagan Roman authorities: holding service in catacombs and holding the bones of the deceased.
Even modern Orthodox tradition holds the relics (bits and bobs from corpses, as well as full ones) of saints in high regard.
Long tradition, we have plenty of oddities to remind us of our too soon coming time. Chandeliers made of skeletons, for example. These things left after death aren’t worshipped but rather a reminder of death to spur people on to using their time remaining wisely, which I think brings down the creep factor but yes, weird to modern sensibilities for sure.
Haven’t read this website but here are some pictures.
I think without even understanding the chant reflecting on the music helps to better understand the intent of these reminders. The music is somber and melancholic yet wishful, it’s conflicted. It presents the intersection of two hard wired things. On the one hand, we profess in an afterlife which, for those in heaven, there is perfect everything and forever and on the other hand the cruelty of death. No one wants to die yet if we truly believe that death is just the beginning of forever and that forever is perfect why would one not desire death in this world of unknowing and misery.
https://wellcomecollection.org/search/works?query=memento%20...