This is yet another of those songs everybody sings and nobody thinks about. Come on, now. Have you ever asked yourself this question? I sure hadn’t.
Once again my good friend Wikipedia put me onto the right track and I’ve gone on from there. As with so many wonderful songs that are entrenched in American music, this one stems from slave spirituals. And, as with the meaning of so many spirituals, it’s a mix of biblical and historical ideas.
When contemporary composer John Muehleisen set Henry Wadsworth Longfellow’s poem “A Psalm of Life” to music, he knew that the poet was not talking about actual weeping numbers in the first line, perhaps a number 7 with tears dripping from the end of the top bar. No. Here the word “number” means a piece, selection, or verse. When we refer to the songs in a Broadway show, for instance, we often call them “number,.” as in “a showstopping song-and-dance number.” Therefore, if we piece together the title, “A Psalm of Life,” the subtitle, “What the heart of the young man said to the Psalmist,” and the first two lines (“Tell me not in mournful numbers/Life is but an empty dream”), we get a message of hope, optimism, and action. 
We know that any true folk song will always have multiple versions, since they weren’t composed in any formal way and were passed down orally for some time before being written. One aspect or the other of the original may be prominent in each variant. “Cindy” has an almost infinite variety of verses and also has the characteristic of having been built at least partly from “call and response,” which in this case has someone start out with a line and then others in the group have to come up with a second line that rhymes with the first, whether or not the lines add up to a coherent story. (This type of activity is also common in some churches in which the preacher says something that is clearly asking for a response, even if it’s just “amen.” My favorite such line is something I heard at a wedding I attended many years ago; when the preacher performing the ceremony started to feel that he wasn’t getting enough feedback, he’d say, “Am I talkin’ to anybody out there?” which would be greeted with a chorus of “amens.”)


The meaning of the the Requiem text, part 4.
The meaning of the Requiem text, part 3:
The meaning of the Requiem text, part two: