Assurance entered Methodist theology through Wesley's own experience of its absence. He had been an ordained clergyman, a missionary to Georgia and a disciplined keeper of religious rules for years before the evening of 24 May 1738, when he attended a meeting in Aldersgate Street, London, and heard a reading of Martin Luther's preface to Romans. By his own account his heart was strangely warmed, he felt he did trust in Christ alone for salvation, and an assurance was given him that Christ had taken away his sins. Before that evening he had kept the outward discipline of religion without the inward confidence Methodist preaching would later insist every believer could have.
That personal history is why assurance became a working expectation rather than a private curiosity in early Methodist practice. Class meetings asked members to describe their spiritual state in language shaped by the doctrine, and lacking assurance was treated as a normal stage to be preached through rather than a permanent condition to be accepted. The doctrine also marked an edge between Methodism and the broader Reformed tradition it grew out of, since Calvinist accounts of assurance more often tied confidence to final perseverance, available in full only in retrospect, while Wesley's version offered a presently felt confidence that could, in his own teaching, coexist with the real possibility of falling away.