A certain person, ‘Ata Muhammad by name, asked Hazrat Mirza Ghulam Ahmad (as) by means of a letter printed in August, 1893, how it could be determined that he was really the Promised Messiah and what evidence there was, if any, of such a Messiah having been promised. Hazrat Mirza Ghulam Ahmad (as) answered this letter by writing this book. Hazrat Mirza Ghulam Ahmad (as) discussed at length the point raised by ‘Ata Muhammad and he established by quoting authentic hadith that the Promised Messiah was to come at a particular point in time. Secondly, he proceeded to establish the facts from the Holy Quran which had spoken about the coming of the Promised Messiah. Thirdly, he discussed whether the hadith and the verses quoted by him were related to him, and he established that he indeed was the true Promised Messiah.
(Taken from An Introduction to the hidden Treasures of Islam)