It is now forty years since this book was written, twenty since it was translated into English, and twelve since the translation was first published. The issues that had caused the author so much concern at the time have become, without exception, all the more pressing today. The need to convey the Islamic concept of Tawhid to the world at large in clear unequivocal terms has been and shall remain a Muslim's first duty. Now that there is renewed worldwide attention towards Islam, it has become even more urgent to convey its core concept, without which there is no religion: The Oneness of God. Key to the Garden is an elaborate exposition of Prophet Muhammad (s) teaching that the inner life must pass through three stages: affirmation of faith with the tongue, then the mind, and finally the heart. The Muslim Testimony of Faith, that there is no deity save God, is at once the essence and the highest principle of Islam. This book is a demonstration, by one of the greatest recipients of the Prophet's heritage of knowledge, of how the whole spectrum of Islamic thought and worship unfolds naturally from these few words.