Two patterns here should attract your attention: the masking of White’s bishop by his knight, and the battery of White rooks on the d-file. Since White’s knight can give check on h6 while unmasking the bishop, everything is in place for a discovery—except a suitable target for the bishop to attack. The knight on d7 won’t do; after 1. Nh6+, g7xN; 2. BxN, White hasn't won anything. So upgrade the target by capturing it with another piece—and then doing it a second time if necessary. Hence the usefulness of having the two rooks on the same file: 1. RxN, NxR; 2. RxN, QxR, and now White has created a worthy target for his bishop. Nh6+ wins the queen after Black fends off the check. In practice, of course, Black probably would play Qb6 on his second move rather than walk into the discovery, in which case White will have won two pieces for a rook.