Almost all the words are still current in modern English, though some are spelled (and in some cases pronounced) differently nowadays. The trick is to read them aloud a few times; much of the mystery will disappear. You can sometimes get the sense of printed Dutch by doing the same thing.

The orthography is Scottish (and note the use of 'jo': 'beloved') but really this differed a lot less than people sometimes think from Northern English of the same period. I think that the attribution to Carver (a Scottish monk and composer of sacred music) may perhaps be questionable. Where did you get the text and information?