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Christian humanism is a philosophy that combines Christian ethics and humanist principles. It regards humanist principles like universal human dignity and individual freedom and the primacy of human happiness as essential and principal components of, or at least compatible with, the teachings of Jesus.
Christian humanism has its roots in the traditional teaching that humans are made in the image of God (Latin Imago Dei) which is the basis of individual worth and personal dignity. This found strong biblical expression in the Judeo-Christian attention to righteousness and social justice. Its linkage to more secular philosophical humanism can be traced to the 2nd-century AD writings of Justin Martyr, an early theologian-apologist of the early Christian Church. While far from radical, Justin in his Apology finds value in the achievements of classical culture. Influential letters by Cappadocian Fathers Basil of Caesarea and Gregory of Nyssa confirmed the commitment to using preexisting secular knowledge, particularly as it touched the material world.
After the fall of the Roman Empire, there were thoughts of a more Christianized humanity for society. Western Christian clerics controlled education, since only the monasteries remained as seats of learning. Charlemagne requested that scholars set up places of learning that would become universities in the 12th century. Eastern Christians meanwhile continued the late Antique practice of studying in the homes of secular masters, studying the same curriculum of classical Greek authors as their predecessors in the Roman period: Homer's Iliad, Plato's dialogues, Aristotle's Categories, Demosthenes' speeches, Galen, Dioscurides, Strabo, and others. Christian education in the East largely was relegated to learning to read the Bible at the knees of one's parents and the rudiments of grammar in the letters of Basil or the homilies of Gregory Nazianzus.
Formal aspects of Greek philosophy, namely syllogistic reasoning, began in the 11th century to inform the process of theology in both the Byzantine Empire and Western European circles . However, during the reign of Alexios I Komnenos (1081-1118) the Byzantine hierarchy convicted several thinkers of applying "human" logic to "divine" matters. Peter Abelard's work encountered similar ecclesiastical resistance in the West in the same period. Nonetheless, Western universities including Padua, Bologna, Paris, and Oxford resulted from the so-called Gregorian Reform, which encouraged a new kind of cleric clustered around cathedrals, the secular canon. The cathedral schools meant to train clerics for the growing clerical bureaucracy soon served as training grounds for talented young men to train in medicine, law, and the liberal arts of the quadrivium and trivium, in addition to Christian theology. Classical Latin texts and translations of Greek texts served as the basis of non-theological education. A primitive humanism actually started when the papacy began protecting the Northern Cluniacs and Cistercians and the Church formed a unifying bond. Monks and friars went on crusades and St. Bernard counseled kings. Priests were frequently Lord Chancellors in England and in France. Christian views became present in all aspects of society, and there was an emphasis on serving God and others. Furthermore, there was a view of human nature that was both hopeful and Christian. All offices, including civil ones, and academic works had religious elements. In addition, religion influenced medicine with the Good Samaritan of the Gospel of Luke. The idea of free people under God came from this time and spread from the West to other areas of the world.
Christian humanism saw an explosion in the Renaissance, emanating from an increased faith in the capabilities of Man, married with a still-firm devotion to Christianity. In this regard, Petrarch (1304-1374) is also considered a father of humanism, being one of the earliest and most prominent Renaissance figures. In his letter "The Ascent of Mt. Ventoux" he states that his climb of the mountain was inspired by Livy, but found its true meaning in St. Augustine's Confessions. His masterful contributions to language and literature triggered the development of studia humanitatis which began to formalize the study of ancient languages, namely Greek and Latin, eloquence, classical authors, and rhetoric. Christian humanists also cared about scriptural and patristic writings, Hebrew, ecclesiastical reform, clerical education, and preaching.
Plain Humanism might value earthly existence as something worthy in itself, whereas Christian humanism would value such existence, so long as it were combined with the Christian faith. One of the first texts regarding Christian humanism was Giovanni Pico della Mirandola's Oration on the Dignity of Man, in which he stressed that Men had the free will to travel up and down a moral scale, with God and angels being at the top, and Satan being at the bottom. Christian principles took effect in places other than Italy, during what is now called the Northern Renaissance. Italian universities and academia stressed Classical mythology and writings as a source of knowledge, whereas universities in the Holy Roman Empire and France based their teachings on the Church Fathers.
Christian humanism finally blossomed out of the Renaissance and was brought by devoted Christians to the study of the philological sources of the Greek New Testament and Hebrew Bible. The confluence of moveable type, new inks and widespread paper-making put potentially the whole of human knowledge at the hands of the scholarly community in a new way, beginning with the publication of critical editions of the Bible and Church Fathers and later encompassing other disciplines. This project was undertaken at the time of the Reformation in the work of Erasmus of Rotterdam (who remained a Catholic), Martin Luther (who was an Augustinian priest and led the Reformation, translating the Scriptures into his native German), and John Calvin (who was a student of law and theology at the Sorbonne where he became acquainted with the Reformation, and began studying Scripture in the original languages, eventually writing a text-based commentary upon the entire Christian Old Testament and New Testament except the Book of Judges, Book of Ruth, Books of Samuel, Books of Kings, Books of Chronicles, Book of Ezra, Book of Nehemiah, Book of Esther, Book of Proverbs, Book of Ecclesiastes, Song of Songs, Second Epistle of John, Third Epistle of John, and the Book of Revelation). John Calvin was the most prominent of the many figures associated with Reformed Churches that proliferated in Switzerland, France, Belgium, the Netherlands, and portions of Germany, Hungary, Lithuania, and Poland. Each of the candidates for ordained ministry in these churches had to study the Christian Old Testament in Hebrew and the New in Greek in order to qualify. This continued the tradition of Christian humanism.
The Enlightenment of the mid-18th century in Europe consolidated the separation of religious and secular institutions that has led to what some consider to be a false rift between Christianity and humanism. But while the Enlightenment crystallized humanism as a distinctly secular, liberal philosophy, it did have sectarian roots that reached back to early 18th-century England. There rationalists known as 'Deists' rejected traditional theology and clericalism in favor of 'natural religion'. Non conformists, they preferred to sidestep the churches and seek God personally by way of reason and innate moral intuition. These Deists triggered a scholarly quest for the historical Jesus which often cast him as a quasi-divine beacon of virtue dispensing homilies that accorded nicely with precepts of bourgeois liberalism. They gave new currency to Christ's humanist ethics and spawned a wave of social gospel liberalism in the 20th century. They effectively reasserted the Judeo-Christian ethic which would play an important role in animating the political and social reform movements of the 19th and 20th centuries. Perhaps the most valuable contribution of this liberal Christianity is that it gave rise to the first British movement for the abolition of slavery, which was founded by the Quakers in the late 18th century. However, it was the Evangelical Christian humanism of William Wilberforce (24 August 1759 - 29 July 1833) that led to the successful abolition of the slave trade.
The carnage of World War I shattered liberal optimism. Boundless idealism was eclipsed by the dark side of humanity and this prompted a realist backlash amongst Christian scholars and theologians. Known as 'neo-orthodoxy', its leading protagonists were Reinhold Niebuhr and Karl Barth. Both were erstwhile political liberals but they now insisted on getting back to 'basics'. The curse of original sin seemed born out by the horrors of the war and any humanist aspirations would now have to be rooted in a theology of redemption and acceptance of complete human dependence on God.
By the 1970s a strident social Christianity had re-emerged. Taking root in the fertile soil of rampant injustice in Latin America and the anti-apartheid struggles in South Africa, 'Liberation Theology' aimed at harnessing Christianity to the cause of social justice and even revolutionary socialism.
Since the advent of postmodernism, some radical 'progressive' Christians  have tended to see the Christ of faith as irreconcilable with the Jesus of history, regarding the latter as a mere mortal and a distinctly fallible one at that. One such writer, Arthur G Broadhurst, argues for a religionless non-theistic form of Christianity: The Christian Humanist: Religion, Politics, and Ethics for the 21st Century, which some Christians see as a logical impossibility. [See also Arthur G Broadhurst, The Possibility of Christian Humanism, Lulu Press, 2013.] As progressives, they generally take a deconstructionist view that dogmatic theology is suspect and spiritual truth is mainly a personalized and subjective pursuit. They tend to align with liberal secular humanism and one of their outspoken advocates is retired Episcopalian Bishop John Shelby Spong.
There have been various attempts to reclaim a more traditional Christian humanism. One of these, represented by the Centre of Religious Humanism and its director Gregory Wolfe, embraces Christianity's rich cultural heritage. This Christian humanism emphasises Jesus as the incarnate fusing of humanity with the divine--humanity in the image of God--especially as manifested in the sublime, creative achievements of Western civilization. These ideas had previously reached their peak in the Renaissance and Wolfe particularly draws inspiration from the Renaissance humanists that supported the Catholic Church, such as Erasmus, Thomas More, Johann Reuchlin and John Colet.