Influenced by the advice of Jeremy Taylor's Holy Living, which he read when preparing for ordination, in Lent 1725 John Wesley began to keep a diary. Unlike his later Journals, this was a private record, though he later drew on it in preparing his Journal extracts for publication. His method changed over the years. In January 1734 he adopted a tabular format, which he referred to as his 'exacter method' and which made possible a concise and detailed record of his spiritual state hour by hour. After the Methodist movement got under way, the diaries became less introspective and more a record of his travels and other activities. He maintained the practice throughout his life, though none of the diaries have survived for the period 1742-1783 and some early ones are also missing.
The diaries were written in a combination of shorthand, abbreviations, symbols and cipher. They were partially decoded by Nehemiah Curnock, who used them in his Standard Edition of John Wesley's Journal; but his work has now been superseded by that of R.P. Heitzenrater in the Bicentennial Edition of John Wesley's Works.
'These diary records, along with other private materials from his pen such as the letters, help us to recall the failures as well as the triumphs, the tedium as well as the excitement, the struggles as well as the strengths, of Wesley's own personal attempts to press on to perfection. Some observers will find his pecular interests fascinating. Many will be intrigued by the sheer energy that his lifestyle exhibits.To some he will seem more than slightly eccentric or compulsive, as he certainly did to many in his own day. To others, the depth of his spirituality and the breadth of his learnng will appear overwhelming.
'The diary does not alter the broad judgments history has passed on John Wesley's reputation. These records reveal him no less of a hero. They detract not an ounce from our admiration for him. But these valuable little notebooks do take us a a bit closer to a more life-like portrait of John Wesley the man.'
Richard P. Heitzenrater, 'Wesley and his Diary', in John Wesley: Contemporary Perspectives (1988) pp. 21-2