I've listened carefully to the version by the Corries, and I have the following thoughts.

I think it's a song about a young man who needs to leave his family and start earning a living. He loves a lassie and wants her to go with him to the place where he's starting - Glenila by bonnie Glenshee. The Corries sing the verse about the snow-covered high hills first, as a way of putting the song in context: answering who and where are these people. It's the nearby hills that will part them, not the sea nor a journey to England to work, so he's not going far.

Why do I think it's about his first job? Because of the verses about men - a shepherd walking, his flock nearby, and soldiers marching, their weapons at the ready. They are men whose place in the world is established, and he wants to be like them. (I can remember times in my younger years, when unemployed and living cheaply on savings, I watched people confidently going about their jobs and felt the same way.)

The verse about the laverock doesn't sit well with me. If the high hills (not just the peaks) are all covered with snow, are birds apt to be about? I doubt it. "Ae" should be "ay", for ae means one and ay means forever. The word "intention", while perfectly legal, jars on my ear as too Latinate. The Corries don't sing this verse, and I'm with them on that. They end the song by repeating the first verse.

I have made sheet music of their version - notes only, no lyrics. If trusted catters want it, you can PM me. Say whether you want it in D (pretty low) or F (flute and recorder-friendly.)