Whereas John Locke (1632–1704) is best known for his "way of ideas" and political theory, he was also a skilled theologian. His theological concerns, interests, and ideas permeate his philosophical, political, and moral thought. Locke’s oeuvre in its different areas is indeed the production of a Christian philosopher. But Locke’s religious views are significant for yet another reason, in that his theological reflections resulted in a unique version of Christianity. Although Locke expounded his religious views in an unsystematic manner, given also his dislike of systems of doctrine and his hostility to claims of religious orthodoxy, an original and internally coherent form of Protestant Christianity emerges from his public as well as private writings. Locke's version of Christianity denotes various similarities with heterodox theological currents such as Socinianism and Arminianism, which Locke knew well. Nonetheless, Locke adhered to the Protestant doctrine of "sola Scriptura," according to which the Scriptures contain all that is needed for salvation. Thus, he always made sure that his conclusions were consistent with, and indeed grounded in, Scripture.

In "The Reasonableness of Christianity," Locke aimed to promote the practice of morality and the development of moral character through a Scripture-based theological ethics. He claimed that his account of Christianity was based on Scripture alone, which he regarded as an authoritative source of historical and eschatological truth entailing moral principles. However, his writings on religion denote many similarities with Socinianism and Arminianism. He adopted Socinus’s proof of scriptural authority, highlighting the excellence of Christ’s moral precepts, insisting on the fulfillment of Old Testament Messianic prophecies in the New Testament, and describing Christ’s miracles as confirming his Messianic mission. This proof enabled Locke to develop a historical method of biblical interpretation, which, stressing the internal consistency of the Bible, considered the biblical texts in relation to both their respective historical contexts and the biblical discourse as a whole. In reading Scripture, he followed the Protestant tradition of the way of fundamentals, but he formulated an original doctrine of the fundamentals of Christianity – that is,repentance, obedience, and faith.

Locke omitted the Trinitarian dogma from his elucidation of the Christian religion in "The Reasonableness of Christianity." This omission implicitly made belief in the Trinity unnecessary to salvation and attracted much criticism, leading John Edwards and others to accuse Locke of Socinianism. Locke refused to clarify his position on the Trinity even when Edwards and Stillingfleet pressured him to do so. His public silence on the Trinity was surprising to many, because the "Reasonableness" appeared in the middle of the heated Trinitarian controversy of the late seventeenth century. Locke actually expressed, unsystematically and at times ambiguously, his views on Christ’s nature and mission in his public writings on religion and in various manuscript notes, and he focused on Trinitarian issues in "Adversaria Theologica" and other manuscripts. His Christological reflections and his consideration of Trinitarian issues denote a heterodox, non-Trinitarian conception of the Godhead, which presents both Socinian and Arian elements, although he never expressly denied the Trinity. Irenic and prudential reasons contributed to his choice to avoid public discussion of the Trinitarian dogma.