Figure[White to move]

You can see the idea here visually by noting the dark-squared triangle between Black’s rook, king, and e-pawn, or by asking what checks White can give with his bishop and what else he can attack at the same time. Either way White would like to play Bxe5 but seemingly is prevented from doing so by the threat of NxB. Ah, but what if that threat is carried out? Lines would be opened by the moves of White’s bishop and Black’s knight. White would have a new check with Rc7—a rook fork which also attacks Black’s queen. If Black moves his king or blocks the check by moving his knight or bishop to d7, White plays RxQ. If Black plays QxR, then White plays QxQ+, and then (after Black moves his king) QxR.