Ah, bread. For most of European cooking, and certainly the cuisine brought over to the Americas by English and French settlers, the leavened loaves are at the very heart of food. Bread is a sign of civilization, a sign of God, a sign of good governance, and for most of history, the literal “staff of life,” without which the people would starve. In Russian, you can say hello by shouting “bread and salt!,” and it’s embedded in the most bread-and-butter English idioms, from “our daily bread” to breadwinners and breadlines.
But “bread” as a word hasn’t been around for all that long, considering. Until around 1200 A.D., when Old English was finishing up its transition to the Frenchified vocabulary of Middle English, the universal word for bread was hlaf, like our modern “loaf.” But unlike the typical story at this point–Germanic Old English word gets pushed out by a Latin/French cognate–English actually switched to another German word for its staple food, one that used to mean something like “morsel,” or “piece”: bread.
Some say that “bread” itself comes from an older root having to do with brewing, in reference to the rising action of the yeast, but it’s more likely to have come from a root having to do with breaking things into little pieces. And once “bread” took over, sticking “loaf” in the corner as a specific type of whole-bread-quantity, the word hasn’t changed (except, unsurprisingly, in spelling–I particularly like the 15th-century “bryead,” which you can imagine said with a bumpkinny drawl).
So that’s where our word for the staff of life came from, but what’s up with calling it “staff of life”? The image is pretty clear–we need bread every day, so it supports us, like a walking staff–but it’s still a pretty clumsy metaphor. After digging a little, though, it starts to make more sense: it’s an awkward translation! It comes from Leviticus, when God is talking to Moses on top of Mount Sinai. After laying down lots (and lots) of rules, about everything from animal husbandry to what kind of oil to use in the Temple, God starts in with the punishments for breaking any of these rules, one of which is “breaking the staff of your bread” (literally, in the Latin, baculum panis). With the breaking in there, the metaphor seems to make a little more sense–even if you don’t lean on bread all the time, you’ll surely fall down without it–but newer translations of the Bible have tended to translate it less literally, as “cut off the supply of bread.”
The metaphor was extended so that bread was “staff of life” by the 1600s, but only in English. Even though they were working from the same source Hebrew, Greek, and Latin texts, the French and German (the likeliest candidates for shared idioms) never took the same semantic leap, and the “staff of life” remains an Anglo-only expression.