Jaythan is a respelling of Jathan, which is a rare name that is found in some translations of the Book of Tobit, which is part of the Old Testament in
Roman Catholic Bibles and the Apocrypha in Protestant Bibles. It is probably just a variation of
Jonathan or
Nathan (click on the linked names to get the original meaning of
Jonathan and
Nathan.)
As for the "spiritual connotation": that is not a matter of etymology or historical origin. The books that give one a "spiritual connotation" of a name are just giving you the author's opinion; there is no authority who decides what the "spiritual connotation" of a name is, it's just the personal opinion of the author. It seems to me that the original meaning of
Jonathan would give an obvious "spiritual connotation" for Jathan or Jaythan. :)