Both 3...Nxe4? 4.Nf5 and 3...Qxe4? 4.Qxe4 Nxe4 5.Nd5 fail tactically for Black.
Preparing Red1, with a pleasant advantage thanks to the opponent's light square weaknesses.
Creating a protected square on d6, which can be exploited by the knight via d2-c4-d6, or even by the rook.
The desired 1...f5 permits 2.exf5! exf5 3.Rd6! with strong pressure; e.g. 3...f4 4.Bd3+! Kh8 5.Bg6+-
After 6...Rb8 7.Nab6 Nf4 8.Nxc8 Rfxc8 9.Nd6 White is also better, but at least material remains even.
Redirecting the idle knight to h6, where it will be helpful in exploiting in the complex of weak squares on g4, f5 and e4.