The Alter Rebbe taught, shortly after he came to Lyozna: One must always (l’olam) be scrupulous (zahir) about the Mincha davening.The special quality of Mincha over Shacharit and Maariv is that it comes in the middle of the day, when people are occupied and busy with their personal affairs, yet they interrupt to daven Mincha. Therefore,l’olam ("always," or more literally: "for the world"), man’s avodain This World is……y’hei adam (lit. "man must be," but the Hebrew words also imply "be a man" i.e. that) his intellect illuminate and affect his emotions….zahir (lit. "scrupulous," but also:) "luminous," i.e., that form (the spiritual) "illuminate" or have dominance over the material. This becomes evident through the Mincha davening.