Parrying the threat of 7 Bxg6, but White's greater piece activity proves decisive anyway.
Quite an unnatural place for the king, but after 3.0-0 Nd4 4.Nxd4 cxd4 , followed by ...Nc6, the absence of the fianchettoed bishop leaves him rather unprotected on g1.
Turning down the rook exchange in view of his space advantage. Besides, the white rook has more prospects on a1 than its colleague on e8, such as Ra1-a6, attacking the b6-pawn.