[Dutchguy]

Pretty mysterious. If this was indeed an encrypted musical piece, why would the builders of the church encrypt it so?

[fireforeffect]

Probably was not encrypted at the time.

Can you read Norse runes? Sanskrit?

Old writing is encrypted if you can not read it. It was not until the finding of the Rosetta stone that Egyptian hieroglyphs and cuneiform were translatable. No one could read them because no one spoke those languages any more.

[RightWhale]

why would the builders of the church encrypt it

Written music is encrypted even now. The encryption is standardized as notation, but when this piece was done the modern standard did not exist. Even so, modern avant-garde composers sometimes use non-standard notation and if you don't know the code nothing but gibberish will result.

[Straight Vermonter]

This may be of interest to you:

http://www.casca.ca/ecass/issues/2005-me/features/turner/Stars%20of%20St_John’s.html

Another example of someone secretly leaving their imprint in a church.