comment: The queen goes back, at the same time attacking g4, defending f7 and preparing ...Re8.
context: 1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. f1b5  3... g8f6  4. e1g1  4... f6e4  5. f1e1  5... e4d6  6. f3e5  6... f8e7  7. b5f1  7... c6e5  8. e1e5  8... e8g8  9. d2d4  9... e7f6  10. e5e1  10... f8e8  11. c1f4  11... e8e1  12. d1e1  12... d6e8  13. c2c3  13... d7d5 So far, everything is very familiar in the theory of the Berlin Defense. White's system is very solid and illustrates one of the problems of Black's opening choice for non-elite players: White plays for two possible outcomes, a perspective that (rightly) doesn't make amateur players very happy with Black's position. 14. b1d2  14... c8f5 Supposedly White plays the bishop to d3 to prevent this move, so putting the bishop on f5 has to be critical against 14.Nd2. 15. e1e3  15... e8d6 Improving the knight's position. 16. h2h3  16... h7h6 A new move. Black has other paths to equality, but this doesn't mean that the position is drawn, as Carlsen never gets tired of demonstrating. 17. a1e1  17... f6g5 The plan of exchanging bishops is typical in this position. 18. g2g4  18... g5f4  19. e3f4  19... f5h7 An inaccuracy, since the bishop is better placed on g6, protecting f7. Black can even play f6-Bf7 later, if necessary. 20. c3c4 Changing the pawn structure. 20... d5c4  21. d2c4  21... d6c4  22. f1c4  22... h7g6  23. e1e5 A pleasant square for the rook. White's pieces are more active, but Black is still very solid. 23... g8f8  24. f4e3  24... d8d6  25. h3h4 White has to be fast in order to create threats.