Parrying both threats at the pawns on e4 and f4. Now if Black installs a knight on e5, White can always swap it off.
Eliminating the opponent's bishop pair and taking the game closer to an endgame, where Black is favoured by his mobile pawn majority.
With the long-term plan of ...Kg7, ...h7-h6, ...g6-g5 and ...f5-f4, whereas White is unable to do the same thing on the queenside.
Swapping queens to reach an endgame where the pawn structure speaks in White's favour.