Why does the return to the home key have greater impact after an unstable development section?

In sonata form, the return to the home key—or tonic—at the beginning of the recapitulation is a pivotal psychological moment because it resolves the intense tonal and thematic conflicts established earlier in the movement.12

The development section functions as an area of tonal flux, frequently modulating to distantly related keys and breaking down themes into fragments. This process creates significant harmonic tension and instability. By the time the music reaches the recapitulation, the listener has been led through a rigorous argument of "tonal flux" and departure from established regularity.345

Consequently, the return to the tonic key provides a sense of "final synthesis" and equilibrium. This reconciliation of opposites is essential to the form, as it allows the listener to perceive the movement's subjects in a new, unified relationship, much like a traveler reaching a summit to view a landscape as a whole for the first time.1