The development of theology in Christendom arose from the need for educated Christians of the ancient world to express their ideas in terminology familiar in current thought. Hence arose the close relation of Christian theology with Greek philosophy formulated by the Greek and Latin Fathers of the Church. St. Augustine, a Latin Father and one of the greatest theologians, introduced and standardized in his writings teachings that became central to Christian theology. Augustine's influence was paralleled in the East by that of Origen.

The great theological problems of the early church involved the relationship of the first and second persons of the Christian Trinity, the relationship of the divine and human in Jesus, and the relationship between God and humanity. One important struggle was over Arianism, the heresy that denied the true divinity of Jesus. The nature of grace was also debated during the Middle Ages and the Protestant Reformation; the heretical Pelagians (see Pelagianism) contended that a human being has the ability to take the first steps necessary toward salvation apart from divine grace. Augustine insisted, against the Pelagians, that humanity is totally dependent on grace for salvation.

Scholastic theology (see scholasticism) sought to illuminate matters of religious faith through intellectual understanding. Scholastic theologians such as Thomas Aquinas attempted to reconcile seeming contradictions in revealed truths by presenting a doctrine with supporting argument, contradicting argument, and a solution. Aquinas' Summa Theologica is often regarded as the greatest work of Scholasticism. Scholastics differentiated carefully between theology and philosophy by confining theology to the field of the systematization and investigation of revealed truths; in this distinction philosophy is to proceed always from reason and does not investigate the truths that transcend reason. The distinction is maintained explicitly by Roman Catholic thinkers and implicitly by conservative Protestants. According to this differentiation Calvinism and Lutheranism are theologies, not philosophies.

As a result of the 18th-century Enlightenment, especially the work of Immanuel Kant, a new rational theology arose in the 19th cent. This must be carefully distinguished from the rationalism of scholasticism, because 19th-century rational theology assumes as axiomatic the ability of reason to criticize adequately every truth. The theological school of Tübingen was the center for the extreme rationalistic theologians, and there the higher criticism of the Bible, which revolutionized much of Protestant thought, was brought to its first fruition. The most profound of 19th-century Protestant German theologians, and perhaps the most influential of the new rationalists, was Friedrich Schleiermacher. The new rationalistic theology developed very rapidly, and hardly any two theologians of it agree in detail; there are various systems of modernism.

In the 20th cent. the Protestant neoorthodoxy movement emerged in Europe and America. It owed much to the theology of Karl Barth and Reinhold Niebuhr. The movement, which accepted the methods and findings of modern biblical criticism, interpreted religion as only one aspect of contemporary life and emphasized faith and revelation as divine gifts. Among Roman Catholics in the 20th cent., liberation theology, which originated in Latin America, has emphasized the importance of fighting oppression and aiding the poor through active roles in political affairs; since the 1980s it has been strongly criticized by the church hierarchy. Under Pope John Paul II, the Roman Catholic Church strongly reasserted its control over the teaching of theology by Catholic theologians, removing official sanction from Hans Küng and others who deviated from church doctrine.