Avoiding 8...Nxe4?! 9.Nxe4, when White gets closer to achieving c4-c5. In the game Black keeps the important c5-square under control, whereas the bishop isn't really doing anything on e4.

Black has no problems.

Preparing Bf5 in order to swap White's good bishop. Besides this, there now appears the threat of ...Bxh3.

This weakens e4 for the rest of the game.

Exploiting the protected square. White's next move makes things worse, but his game was difficult anyway.

With strong pressure.

By attacking the d6-pawn White prepares 2 Bf3 in order to swap bishops, after which the weaknesses on d5 and d6 will become easier to exploit.

4...f5 seems preferable, preventing Ne4.

Since the plan of tripling the major pieces would leave the c4-pawn in danger, Karpov prefers to open a new front on the kingside.