a) The Vikings didn't stick to coastal areas; Ireland is full of rivers, and their longboats could sail in three feet depth of water. Illuminated manuscripts were enormously valuable and very, very tradeable, a real prize - equivalent to stealing a Picasso today. Monasteries were where these, and also stores of beautifully worked gold ornaments, were kept, so they were a prime target.

b) The books were also regarded as somehow magical by many people, and were often carried into battle to protect the particular grouping that carried them - especially one particular one, known as the Cathach...but that's another story.

c) The psalms were differently numbered then, and the psalm on which the book was open was in fact one about earth being a "vale of tears", which is certainly no word of a lie.