"Moderato con grazia" is the last A section that returns to the themes set in A. After recapitulating the "walking" themes, Gershwin overlays the slow blues theme from section B in the final "Grandioso".
The final A section, "Moderato con grazia", revisits the concepts established in A, after summarizing the "leisurely" themes. Gershwin subsequently overlays the slow blues motif from section B onto the dramatic "Grandioso" in the concluding movement.