Interpretation
There are many theories about the meaning of the song. One interpretation based on the lyrics is that the song is sung by the lover of a captured Jacobite rebel set to be executed in London following a show trial. The heads of the executed rebels were then set upon pikes and exhibited in all of the towns between London and Edinburgh in a procession along the "high road" (the most important road), while the relatives of the rebels walked back along the "low road" (the ordinary road travelled by peasants and commoners). Another interpretation of the 'Low Road' is that it refers to the traditional underground route taken by the 'fairies' or 'little people' who were reputed to transport the soul of a dead Scot who died in a foreign land - in this case, England - back to his homeland to rest in peace.
Another similar interpretation also attributes it to a Jacobite Highlander captured after the 1745 rising. The Hanoverians played games with the Jacobites, and said that one of them could live and one would die. This is sung by the one who was sentenced to die, the low road referred to being the passage to the underworld. Some believe that this version is written to a lover who lived near the loch.
A related interpretation holds that a professional soldier and a volunteer were captured by the English in one of the small wars between the countries in the couple of hundred years prior to 1746. Volunteers could accept parole, a release contingent on the volunteer's refusal to rejoin the fighting, but regulars could not and so could face execution. The volunteer would take the high road that linked London and Edinburgh while the soul of the executed regular would return along the "low road" and would get back to Scotland first.
Read more about this topic: The Bonnie Banks O' Loch Lomond