An unusual move for those that follow GM theory but not that uncommon otherwise.

I was happy to allow the exchange as this is Black's best bishop and the recapture gains me a tempo.

Protects c4, although I doubt that Black could hold the pawn if he took it after Qxd2.

Here I was thinking I could play Nd2-f3 and strong point on e5. Winning the "minor exchange" with NxB also comes into consideration at the cost of a tempo.

Developing the Knight in front of the c pawn is supposed to be strategically suspect in Q pawn Openings on the grounds that the c pawn is required to attack white's centre by c5. However sometimes Black has the opportunity to play e5 in things like the Winawer counter gambit or Chigorin's Defence.

White returns the tempo and takes the minor exchange. Probably Nd2-f3 was better.

Nf3 would have prevented e5.

After some calculation. White tries to avoid being saddled with an isolated Q pawn as he only has two minor pieces to support it, and also has to be careful about the bishop being exposed to a discovered attack from Black's Queen.

Black takes the bishop. White has the king-side pawn majority and extra centre pawn. Black has a tiny lead in development.

This stops the double attack on g7 and a7 by Qd4 and also keeps the knight out of e5.