(Painting of the Galil by Lael Har)
The essence of a shul's holiness is drawn down from the holiness of Eretz Yisrael, for in Eretz Yisrael is the essence of the ascent of prayer, as it is written, "and pray to You toward their land." (Melachim I 8:48) And the essence of the holiness of Eretz Yisrael is through, "He has declared to His people the power of His works." (Tehillim 111:6) This corresponds to what Razal relates, "He took it [Eretz Yisrael] from them and gave it to us," (Rashi on Bereishis), for through this we have to power to sanctify every place in the word with the holiness of Eretz Yisrael. As such, the holiness of a shul draws upon the concept of conquering Eretz Yisrael, for through, "He declared to his people the power of His works," they were able to conquer the land. And therefore through building shuls and batei midrash for the sake of Heaven, the way one must act, walk, and return to our holy land, and to conquer it from the hand of the Sitra-Achra is drawn down to us even now.