I'm told this song, like a lot of "Negro spirituals," was very much connected to the underground railroad and the desire/hope to escape bondage. This makes a lot of sense to me, considering the lines our choir sings:

Keep your lamps trimmed and burning,
The time is drawing nigh.
...
Children, don't get weary,
The time is drawing nigh.

Those lines could be about being ready for heaven or for the second coming of Christ or about being ready when the right time comes for escaping from the plantation.