Musar do Izajasza 62:7

I have found in the book Ba-assarah ma-amorot chapter 3, an article that explains the source of this legislation. The author writes as follows, quoting Isaiah 62,6: "Upon your walls O Jerusalem, I have set watchmen." These are four watchmen corresponding to the four-lettered name of G–d, their דינים are three, since the watchmen of the "Upper World" never abandon Jerusalem, and concerning them the prophet says "all day long and all night long" (ibid.). They are never without supervision.