White has a number of offensive ideas here that become fatal only when combined. The first involves his knight’s attack on g7, which traps the Black king on the eighth rank; as a result White almost can mate with Rd8, but Black’s rook on f8 stands in the way. The second idea involves White’s queen. It can’t reach the back rank, but White can do better by playing QxN+ (examine every check), forcing RxQ to prevent Qg7#. Now White can play Rd8+, and Black’s interpositions with his queen and rook both are useless. The threats posed by White's queen and rook here are pretty obvious, but the knight on f5 is equally indispensable. When one of your pieces seals off a flight square for the enemy king as White’s knight does here, it is important to take notice and experiment with back rank mating ideas.