Reinforcing the knight and preparing Qc3, d3-d4 and c4-c5 with a further attack.
This just helps White in opening lines towards the black king. 1...Be6 was safer, preparing to meet 2.g5 by 2...Nd7.
5.Bxh7+! Kxh7 6.Rh2+ Kg8 7.e4 dxe4 8.fxe4 Qe7 9.Qh5 Qxe4+ 10.Ng2 f5 11.gxf6