Possibly one of the reasons why Holy Island may be so sacred is that it would appear to be the terminus point for an earth energy line that travels up from St.Catherine's Hill in Sussex, through Arbor Low stone circle in Derbyshire and which ends up at Lindisfarne.
'Serpenteer' - a reader on my blog 'Hedge Druid' - recently validated this information by dowsing it on a visit thee, and pinpointed the exact location of the line. The comments attached to this blog post (http://www.hedgedruid.com/?p=4554
) give you the detail if you are interested in that kind of thing. Might make your stay more enlightening?
Personally, I can't wait to go there myself and find out why it is so special. Hope you enjoy your visit and have fine weather for it.