Joe, it's my understanding that the song was written following an important speech by politician Harold MacMillan in 1959 when he spoke of the 'wind of change' that was blowing over Africa as former colonies gained independence -- which then makes more sense of the final couple of the lines about the 'black boy frae yont Nyanga' (a South African township, I believe).

And while I'd love to be singing it as a Scottish anthem, I've always thought of it as a song of international solidarity.

Finally, I love the line which offers 'breid, barley bree and painted room' as necessary hospitality -- sustenance, conviviality and beauty/culture.