Protestant theology represents not so much a new departure as an emphasis on and a reinterpretation of certain ideas that were always present in Christian thought but not always stressed. Luther and Calvin evolved their theology largely from two sources, the writings of St Paul and St Augustine. In doing so they turned away from the rational theology of medieval Catholicism, especially as represented in the thirteenth century by St Thomas Aquinas, who had tried to reconcile Aristotelian philosophy and theology, reason and faith, man and God, in a harmonious, hierarchically ordered system. Instead they emphasised, as Augustine and some fourteenth-century Augustinians had done, the basic paradoxes of Christianity, the limitations of human reason, the great gap between man’s sin and God’s grace. Important sources were Paul’s Epistles, especially Romans and Galatians, Augustine’s City of God, his later writings against the Pelagians (see below), for example On the Spirit and the Letter and On Grace and Free Will, and the Enchiridion (handbook) in which he summarised his teaching. Luther and Calvin propagated and popularised their reinterpretation of Paul and Augustine in a large number of works written in Latin for ecclesiastical readers and in German and French for laymen; of these the most important are Luther’s The Freedom of a Christian (1520), On the Bondage of the Will (1525), his many commentaries on the books of the Bible, especially the Preface to Romans (1522); and Calvin’s Institutes of the Christian Religion (several editions both Latin and French, 1536-60). Lutheran and Calvinist ideas were diffused in England both directly through translation, for example, Tyndale’s versions of Luther’s commentaries (15, 26), and, indirectly but more widely, through incorporation in other men’s books. England produced no comparable original theologian, yet the vast religious literature of all kinds and purposes-sermons, controversial writings, catechisms, handbooks of devotion and practical piety, theological textbooks-made every reading Protestant familiar with the ideas and terminology of the continental reformers.