Last move in book.

Preparing the fianchetto, with plans to castle king-side.

Moving the knight onto the newly closed d-file, while taking aim at the strong bishop on e5.

b4 might be an even stronger square for the knight. After a potential 18. Qxe7 Nxd3 19. Rxd3 - whites rooks are no longer doubled on the back rank.

Taking more of an immediate material advantage, at the cost of a misplaced queen. However blacks position is still well enough defended.

21. Ra1 looks even stronger here, as black must then immediately play c5 themselves to create a path for the queen to escape.

The capture on c6 seems premature, as white can't win back material directly, and is left positionally worse. 25. Be4 is a better choice to hold the position here, adding a second attacker to the c6 square, and adding complications for black's a8 rook.

An out-and-out miscalculation, after 27. Be4 white would be better. The more accurate square for the queen was g5, holding a slight advantage in the position.

Moving the knight here allows black to double the b-file, causing all sorts of unpleasant issues for white.