What pieces can White’s bishop threaten? Bxd5 attacks the rook on a8 and aims the bishop at Black's king. Or a visual way to assess the position is that it is a classic example of a king-and-rook triangle that lends itself to a fork at d5. Either way you look at it, the trouble is that the pawn on e6 blocks the way to the king and guards d5 as well. The point is clear: the pawn must be vacated from that square. Moving an enemy pawn off a square is best done by capturing something it protects. Here it protects the knight at f5; so 1. RxN, 2. e6xR does the trick. Now Bxd5+ safely attacks king and rook, picking up the latter next move and netting a piece.