Rabbi Isaiah Horowitz (1565-1630), known as the Shlah from the name of his chief work (Shnei Luḥot HaBrit – The Two Tablets of the Covenant), was a rabbi in Central and Eastern Europe and later Chief Ashkenazi Rabbi of Jerusalem. This text is an excerpt from his kabbalistic prayer book, Siddur Shaar haShamayim (Gate of Heaven), which deals with the Shma prayer.