Comentario sobre Deuteronómio 18:5

לעמד לשרת TO STAND TO MINISTER — From here we may derive the law that the sacrificial service must be performed standing (Sifrei Devarim 167:1; Sota 38a).

כי בו בחר ה' אלוקיך מכל שבטיך, and it is therefore called for that you provide him with food and clothing in order that he will be free to perform the Temple service on your behalf.

לעמוד לשרת, “to stand and perform service.” This verse teaches that service in the Temple must be performed while standing. The reason the Torah adds the word בשם before writing the tetragram is that the word בשם is a reference to the attribute of Justice. It occurs in that form repeatedly, such as in Exodus 20,21 אזכיר את שמי, “I allow My name to be mentioned,” or Deut. 12,11 לשכן שמו שם, “to provide a residence for His Name there.”
Onkelos also feels that every time that the word שם appears in connection with the name of G’d it indicates the Shechinah, i.e. a form of the attribute of Justice. This verse (“to stand and serve”) is the source of our sages saying that the High Priest would pronounce the 42-lettered name of G’d on the Day of Atonement seeing that day is one when the attribute of Mercy is co-opted to the attribute of Justice. The letter ב and מ in the word בשם equal 42, whereas the letter ש =300 is the numerical value of the tetragrammaton when the aleph bet is read backwards i.e. א=ת, ב=ש, ג=ר, etc. (We have mentioned repeatedly that whenever the letters in the tetragrammaton appear in the reverse order this signifies the Justice aspect of that attribute. Here you would get מצפ'ץ). You will note that this paragraph has 42 words, just as the first benediction of the Shmoneh Esreh prayer (better known as עמידה), prayer-service to be performed while standing.