Just before the Great Awakening, a young George Whitefield, yet unconverted, was given a small book entitled, “The Life of God in the Soul of Man,” by Henry Scougal. A young Charles Wesley, a member of the Holy Club, and not yet converted himself, gave George the book that would forever change His life, genuinely introducing Him to the true Jesus of the Bible, and thereby sparking a flame that would be used to convert thousands upon thousands of souls in the Great Awakening.
This message by John Piper is a wonderful help as well.
You can purchase the book at Grace and Truth Books, or using this link to Amazon, have 5% of the purchase donated to Strategic World Impact.