Is there any significance to Risei's line?
This is just some unimportant ritual Risei thought up, possibly because he cared for the symbolism (being a devout priest), or that it might accentuate and reinforce his role as overseer.  You'll see implicit evidence of this in later episodes:


   After Risei is killed, Kotomine takes the command seals.  He has to recite a specific verse of scripture to do this, thus reinforcing how Risei likes to add his faith into the things he does.  He later convinces Kariya to use two of his command seals to kidnap Irisviel, on the promise that Kotomine will give him another fight with Tokiomi, as well as the grail at the end of the war.  He wonders if it was really worth two commands, and Kotomine assures him that there is nothing to worry about.  He simply places his hand over Kariya's command seal marks, and they are restored in a (literal) flash, and nothing more.