"The outbreak of war in 1562 was the culmination of a decade of extraordinary growth in French Protestantism. There may have been two million adherents in around a thousand congregations by 1562, while in the early 1550's there had been only a handful of secret groups...How had such rapid expansion taken place? Public preaching had not been possible on a significant scale to spread the messgae in France; there had not been enough ministers, and limited opportunities to gather to listen to sermons. Books played major part, but the two central texts, the Bible and Calvin's Institutes, were bulky and expensive...The explanation for this mass lay activism may lie in the one text which the Reformed found perfectly conveyed their message across all barriers of social status and literacy. This was the Psalter, the book of the 150 Psalms, translated into French verse, set to music and published in unobtrusive pocket-sized editions...In the old Latin liturgy the psalms were largely used in monastic services and in private devotional recitation. Now they were redeployed in Reformed Protestantism in this metrical form to articulate the hope, fear, joy and fury of the new movement. They became the secret weapon of the Reformation not merely in France but wherever the Reformed brought new vitality to the Protestant cause...The metrical psalm was the perfect vehicle for turning the Protestant message into a mass movement capable of embracing the illiterate alongside the literate...The words of a particualr psalm could be associated with a particular melody; even to hum the tune spoke of the words behind it, and was an act of Protestant subversion...The psalms could be sung in worship or in the market-place; instantly they marked out the singer as a Protestant, and equally and instantly united a Protestant crowd in ecstatic companionship just as the football chant does today on the stadium terraces."

-- Diarmaid MacCulloch, The Reformation (New York: Penguin, 2003), 307-8.