Everything about "pox leber" as a minced oath, and an earlier source.

[MarcoP]

I guess that peyorant is a weird spelling for perjurant. So the last passage could mean:

"Thirdly, it is clear that still more blameworthy are those who swear by things that neither exist nor will exist, thinking themselves not bound [by their oath], such as those who say 'sam mir pox gamiger gamer' [curse me by the goat’s torment of torments]. For no goat has the torment of torments, nor does God shine forth in these words [since they are meaningless]. Therefore they seem to sin doubly: because they commit perjury and because they invoke as witness something that can testify neither in itself nor through [God] shining forth in it."