The song is about too many birds sitting on one tree (which of course is a metaphor for too many people in one place fighting for the same thing). In the end there is no place for the one black bird and he has to go and sleep on a stone, which gives him no real rest. Each day he keeps return to the tree but only finds it full and has to return to the stone.
I'm not sure what the last bit means but I think "If you could only stop your heart beat for one heart beat. " is describing the birds desire to rest, he wishing that his heart could rest just for an instant.
The song is about too many birds sitting on one tree (which of course is a metaphor for too many people in one place fighting for the same thing). In the end there is no place for the one black bird and he has to go and sleep on a stone, which gives him no real rest. Each day he keeps return to the tree but only finds it full and has to return to the stone.
I'm not sure what the last bit means but I think "If you could only stop your heart beat for one heart beat. " is describing the birds desire to rest, he wishing that his heart could rest just for an instant.