The temptation in the wilderness MAT 4:1

Immediately after the voice at the river, the Spirit leads Jesus into the desert, where he goes forty days without food. At the end of that time three suggestions are put to him, and each one is met with a sentence from Deuteronomy rather than a direct refusal.

The verses he quotes are words originally given to Israel in its own time in the wilderness, words Israel had not kept. By answering with them, Jesus is shown living out in his own desert what the people failed to live out in theirs.

The point often missed is that none of the three suggestions sounds crude or absurd. Turning stone to bread when genuinely starving, trusting you are protected by jumping, or gaining the kingdoms without the cross are each framed as reasonable, even sensible, which is what makes them real temptations rather than obvious traps.

The forty days set the physical reality behind the first suggestion, since by then Jesus is genuinely starving, not merely tested in theory. The number also recalls Israel's long stretch in the wilderness, the very setting from which the Deuteronomy verses he quotes were first spoken.