Psalm 91 was very famous and well-used, and quoting verse 12 naturally sent you into verse 13. But at this point, the Devil stops. In a sense, he has already said far too much, because any reader of the Psalm knew what came next, and what horribly bad news that was for Satan and his cause. Of course he stops there, because this next verse proclaims the fall of evil forces (like himself), and moreover it contained what were at the time read as evocative messianic references to trampling and serpents.
Naturally, thought some commentators, the Devil would not want to undermine his argument by citing such an embarrassing line. Origen noted this failure to follow through. Incidentally, he also thought that Satan had committed an “exegetical blunder” in suggesting that the Son of God would actually need the help of angels to accomplish anything.
So where did verse 13 go? Why did Jesus not hit Satan back with it? It makes the whole story annoyingly incomplete, and even mysteriously so. In fact, however, if we read Luke’s gospel as a whole, that very v. 13 shortly reappears, centrally and memorably, as Jesus openly proclaimed his messianic mission. Jesus caps Satan’s quotation.
When we read the story of the temptations and the wilderness, we normally read an ending at Luke 4.13: “And when the Devil had ended all the temptation, he departed from him for a season.” But that is not the end of the story. Satan and Jesus would meet again, and sooner in the story than we might expect.