Understand that Ein Sof, blessed be He, is the mystical meaning of that initial thought, as the whole of creation, in its final, completed state, was already manifest before Him. However, the metaphor is not exactly precise, since for Him the future and present are the same. Additionally, the thought itself is the completion, as unlike us, He does not require practical tools to complete the construction. Consequently, in Him it is actual reality. Accordingly, the world of Atzilut is a mystery27"Mystery" here means it is hidden away, like the design in one's thoughts. like the design in one’s thoughts, with all of its details, which will later have to become manifest when the builders actually start building the house.