What's the best move by white in this game? In this game white must win. Please help me.
The key move is the g3 move.


If the e3 rook is unpinned, black has lot's of troubles
If the b8 knight is under-protected, Qxb8 wins easily


1.g3 achieves both.

 1.g3 Qc7 2.Rxd7 now wins (Qxb8 or Rxe8 coming)


Black should resign.