R. Naphtali Hertz claims that he brought back the sources of R. Luria's Kabbalah with him from Erez Israel, where he supposedly lived for some time. He accused R. Joseph Solomon Delmedigo who he claimed had been his pupil, of transcribing kabbalistic manuscripts which were in R. Naphtali Hertz's possession, and then publishing them, with noticeable distortions, in his books Ta'alumot Hokhmah (1629) and Novelot Hokhmah (1631). However, the contrary seems much more likely; that it was R. Naphtali Hertz who culled from R. Delmedigo's work as well as from many other sources. While R. Delmedigo's interest lay in the abstract philosophical aspect of Kabbalah, which he attempted to explain to himself, R. Naphtali Hertz appears as an enthusiastic and fanatical kabbalist, with a special flair for the mystical and non-philosophical traits of Kabbalah - in R. Isaac Luria's Kabbalah as well as in the Kabbalah of the early kabbalists. This accounts for the strong emphasis given to such elements as the doctrine of the Sitra Ahra ("Other Side" - the Evil) and demonology. He wove the old kabbalistic themes together with the later ones in an elaborately detailed style. R. Bacharach claims to derive his teachings from the books of R. Hayyim Vital, although important chapters of his doctrine, such as his version of the doctrine of Zimzum ("Withdrawal") and all it entails, are completely foreign to R. Vital's writings. The merger of both these traditions characterizes this book, written with talent and clarity. R. Naphtali Hertz also borrowed liberally from certain parts of Shefa Tal by R. Shabbetai Sheftel Horowitz (1612). His style is pervaded by messianic tension. The book Emek ha-Melekh had a great impact on the development of the late Kabbalah. It was widely recognized as an authoritative source on the doctrine of R. Isaac Luria and kabbalists from many countries, especially Ashkenazim, the great Habad Hasidim, and the school of the Gaon R. Elijah b. Solomon Zalman of Vilna, quoted him extensively. His influence is also noticeable in R. Moses Hayyim Luzzatto's system of Kabbalah, and in the book Kelah [138] Pithei Hokhmah. On the other hand, strong criticism of the book was soon expressed. Already in 1655, R. Hayyim ha-Kohen of Aleppo, a disciple of R. Hayyim Vital, in the introduction to his book Mekor Hayyim (1655), protested against R. Naphtali Hertz's claim of being the true interpreter of R. Luria's doctrine. The protests of R. Benjamin ha-Levi in his approbation to Zot Hukkat ha-Torah by R. Abraham Hazkuni (1659), and of the preacher R. Berechiah Berach, in his introduction to Zera Berakh (2nd part, 1662), against misrepresentations of R. Luria's Kabbalah were also intended for R. Naphtali Hertz. R. Moses Hagiz says in Shever Poshe'im (1714) that Emek ha-Melekh is called Emek ha-Bakha ("Valley of Weeping"). R. Isaiah Bassan complains to R. M. H. Luzzatto about the numerous translations of chapters from Emek ha-Melekh in Latin referring to the Kabbalah Denudata by Knorr von Rosenroth "which were among the important causes of prolonging our exile" (Iggerot Shadal, 29). R. H.J.D. Azulai also wrote: "I have heard that no genuine writings got into his (R. Naphtali Hertz's) hands... therefore the initiated refrain from reading either it or the Novelot Hokhmah." In Emek ha-Melekh there is a reference to many other books by R. Naphtali Hertz concerning aspects of the kabbalist doctrine. Of these only a part of the Gan ha-Melekh on the Zohar is extant in an Oxford manuscript.

ראינו טופס עם שער אחר, השונה בקישוט, בדפוסת ובפרט-השנה: "נדפוס [!] בית אורי וייבש ב"ר אהרן הלוי ... בשנת מושיע את עמי [תכ"ו]". באמת זו הוצאת ת"ח שלפנינו, ורק השער הוחלף. אורי וייבש הלוי עבד מקודם כפועל בדפוסו של בנבנשתי (נזכר גם בקולופון) נעשה אחר כך מדפיס בעצמו והוציא בשנת תכ"ו מספר טפסים שהיו מונחים במחסנו, עם שער חדש ובו פרט המרמז על שבתי צבי. עיין: ג' שלום, קרית ספר, ל, תשט"ו, עמ' 413 (עם צילום השער השונה); שבתי צבי, א, תל-אביב תשי"ז, עמ' 54-56; שם, ב, עמ' 437. דף י,א-טו,א (בספירה הראשונה): שער מעשה ניסים של ... האר"י זלה"ה (פרק א-יג). הוא "שבחי האר"י", נוסח שלמה שלומיל מדרזניץ. עיין: מ' בניהו, תולדות האר"י, ירושלים תשכ"ז, עמ' 67-60.

הסכמות: ר' יום טוב ליפמן לוי העלר, [קראקא], ראש-חודש אייר ת"ו; ר' יושע ב"ר יוסף, קראקא, ראש-חודש אייר ת"ו; ר' יודא ב"ר יצחק המכונה זעלקלה מזיא אשכנזי, קראקא; ר' שבתי ב"ר ישעיה סג"ל הורוויץ הנקרא שעפטל, פוזנא; ר' מנחם מענדיל ב"ר יצחק ר' אביגדורש [באס], ורנקפורט, כח אייר ת"ז; ר' נפתלי הירץ ב"ר יצחק אייזיק גינצבורג, פוזנא; ר' יעקב ב"ר אורי הכהן, המכונה ר' יעקב שיף, ורנקפורט; ר' עזריאל ב"ר יצחק ברילן, ורנקפורט, כח אייר ת"ז; ר' נתן ב"ר יצחק יעקב בון ממגנצא, ורנקפורט, ז תמוז ת"ז; ר' יודא ב"ר שמואל רויטלינג מילר, בינגא, ת"ז.