White has the familiar powerful coordination of his pieces—a queen and bishop trained on the key square at the corner of the king’s pawn cover: c7. Here as before, this isn't enough to mate by itself. But there is more: a rook on the f-file. So the queen and bishop can be used to extract and then pin the queen that guards Black’s back rank: 1. Qxc7+, QxQ and now 2. Rf8# follows.