There is a classic pattern in which a rook on its first rank—here the f1 rook—slides out onto an open file to pin the enemy queen. One reason the pattern is common is that a rook on the first rank often has automatic protection already in place from its fellow rook, or the queen, or the king, giving it the protection it needs to go after the enemy queen. In this case White sees Black’s king and queen adjacent on the e-file, and he has a rook he can move to that file with protection from his other rook. With those elements in place, the presence of White’s own knight on e5 becomes an opportunity rather than an obstacle: it can take something, and if Black spends any time recapturing it White then can play Re1. White spends his free move with the knight playing a capture: NxN. Black can’t afford to recapture, as he must act to avoid the pin Re1.