Preventing Rb1+ and preparing 12 Ra5 with an attack on the a7-pawn. The latter also enables a future c4-c5 with a huge advantage.
Preparing ...Bc6 and ...Nd7 in order to improve the bishop and step up the pressure on the e5-pawn.
In contrast, 1...Nb4? runs into 2.Nd6+! cxd6 3.Qxb4 with a clear white advantage – Karpov.
After 4.Nxd7 Rxd7 Black has a long-term edge thanks to the weak e5-pawn, so White opts to transform the position.