The idea is after 1.Ngxe5 dxe5 2.Nfxe5 white is threatening a knight fork that black has to do something about and there's this hidden pressure on e7.
2...Be8 3.Bxf5 Rxf5 4.Nc6 Bxc6 5.dxc6 Na5 6.Qxe7
2...Qe8 3.Nxd7 Qxd7 4.Bxf5 Qxf5 5.Qxe7 Qxf2+ 6.Kh2
2...Bf6? 3.Nxg6+ Kg8 4.Nxf8 Bxc3? 5.Nxd7 Bxa1? 6.Qe6+ mate is coming