The Life of God in the Soul of Man: Real Religion by Henry Scougal and published by Christian Focus Publications.
This timeless classic was originally written to encourage a friend and stimulate his spiritual life. It was so appreciated that it was later published as a book for a wider readership. A hundred years later a copy was sent to George Whitefield by his friend, Charles Wesley - it was instrumental in Whitefield's conversion. This book provided much of the stimulation behind the Methodist Revival of Britain and the Great Awakening in America. In it Scougal explains the four essential characteristics of divine life, their excellence, their advantages and the practical steps that you can take in realising them as your personal experience.