Carryover cooking
Carryover cooking is the continued rise in a food's internal temperature after it is removed from the oven, caused by residual heat travelling from the hot outer layers toward the cooler centre.
In a pie the effect is modest but useful: the filling near the crust is hotter than the middle, and during a rest the temperatures even out while the centre climbs a few degrees, typically 2 to 5C (4 to 9F). This is one reason a pie that looks barely done at the edges can be fully cooked after resting.
Resting also lets a thickened filling cool from a thin boil to a sauce that holds together when cut. Give a large pie 10 to 15 minutes out of the oven before slicing; it will still be plenty hot.