To create the "Messiah" libretto Charles Jennens, a formidable scholar and a friend of Handel's, compiled a series of scriptural passages adapted from the Book of Common Prayer and the King James Version of the Bible. As a traditionalist Christian, Jennens was deeply troubled by the spread of deism, the notion that God had simply created the cosmos and let it run its course without divine intervention. Christianity then as now rested on the belief that God broke into history by taking human form in Jesus. For Jennens and others, deism represented a serious menace.
Deists argued that Jesus was neither the son of God nor the Messiah. Since Christian writers had habitually considered Jews the most grievous enemies of their religion, they came to suppose that deists obtained anti-Christian ammunition from rabbinical scholars. The Anglican bishop Richard Kidder, for example, claimed in his huge 1690s treatise on Jesus as the Messiah that "the deists among us, who would run down our revealed religion, are but underworkmen to the Jews."
Kidder's title says it all: "A Demonstration of the Messias, In Which the Truth of the Christian Religion Is Proved, Against All the Enemies Thereof; but Especially Against the Jews." Jennens owned an edition from 1726, and he appears to have studied it carefully. Kidder's work reads like a blueprint for "Messiah."
Jennens had the discernment to see that he couldn't thwart his adversaries simply by producing reading matter insisting that biblical texts be understood both typologically and as Jesus-centered. Like Arius, who won popular opinion for his views with catchy anti-orthodox jingles in the fourth century, Jennens resorted to music, approaching Handel with his libretto.
What better means to comfort disquieted Christians against the faith-busting wiles of deists and Jews than to draw on the feelings and emotions of art over and above the reasons and revelations of argument? "Messiah" does exactly this, culminating in the "Hallelujah" chorus.