Black has a loose bishop at c6. White’s queen has one safe, plausible way to attack it: Qc2. If the Black king could be drawn onto g6, a fork of king and bishop would be possible. White’s bishop can help by taking the pawn at g6, giving check and taking a piece that only Black’s king protects. If Black replies KxB, the board is now arranged for a queen fork with Qc2+, gaining White a pawn.