The whole history and progress of Christianity verifies these two facts. There has been great _Diversity_ in the numerous developments of the Christian religion which we find over the face of the whole earth, and it has often entailed deplorable strife. But Christian _Unity_ has never ceased to be the fundamental principle of these different manifestations, and _Universality_ has remained the ultimate aim of Christianity, in spite of the different methods which it has adopted and forms in which it has been clothed, as it has spread from land to land. In Europe, and in the states which have grown out of European colonies, Catholicism and Protestantism are the two great branches which have sprung from the Christian stem. For a long time a grievous and sanguinary war was waged between these two Churches. They triumphed or succumbed on different battle-fields. But where Catholicism has conquered, as in France, Protestantism has not perished; where Protestantism has been the victor, as in England, Catholicism still survives. After having subjected each other to so many trials and so much suffering, these two Churches have at last learnt that they can and ought to live together in peace, and that liberty must be their watchword and their safeguard. From the brightest epochs of Catholicism and Protestantism, I have endeavoured to select some of their most earnest and noble representatives,--men whom no intelligent and well-informed man of the present day can refuse to recognise as Christians. {3} I was born a Protestant, and the experience of life, as well as the study of history, have more and more confirmed me in the faith of my forefathers; but, at the same time, they have taught me to recognise and to revere those true Christians who are members of Churches not my own. The thirteenth and the seventeenth centuries are the two noblest and fairest epochs of French Catholicism. The sixteenth century and the beginning of the seventeenth are the two noblest and fairest periods of French Protestantism. Among French Catholics I have chosen St. Louis in the thirteenth century and St. Vincent de Paul in the seventeenth, as two great and noble Christians, two earnest and illustrious representatives of the Christian faith and life, as well as of the loftiest thought and purest morality of their country and their generation. Among the Protestants of the sixteenth century, Calvin and Du Plessis Mornay present the same characteristics, and deserve an equal glory. These four men were emphatically and first of all Christians, in thought and life. Christian faith and piety shone out in all of them, notwithstanding their profound divergence and their fierce controversies. That is why I have selected them; and I have tried to depict them as glorious and profitable examples of Christianity, and of its persistent _Unity_ in the midst of its most striking _Variety_. Guizot. Val Richer, 1868. {4} {5} St. Louis, King Of France.