Almost 350 years ago Joseph Alleine wrote this book (published at that time under the title An Alarm to the Unconverted) to spur non-Christians into serious consideration of Christianity and Christians into serious consideration of active evangelism. He clearly defines what Christianity is - and is not - while impelling the reader onward with references to Scripture abounding. He accurately depicts the sinner's situation and the appropriate Christian response to it. The clarity of his words has only grown more lucid over the centuries, and still speaks to believers and unbelievers alike.
One of the greatest evangelistic books, and a spur to personal evangelism.