Figure[White to move]

Here is a similar position with a bit more to see. What mating threats does White have? The usual: he has the standard bishop attack on g7; White will have a fork if his queen can attack g7 and a loose piece at the same time. Queen moves to c3, d4, and g5 all are possibilities; the move to d4 looks promising here because it attacks the Black bishop on e4 while also still protecting the White bishop on b2, which you see is under attack. As for Black’s bishop, it isn’t loose but it is protected once by a rook and attacked once by a knight. So if White plays Qd4 and Black replies with some move to fend off the threat of mate, White then will be able to play NxB with impunity.

Except that "impunity" is a little too strong. For here is the new wrinkle to observe: after White plays NxB, Black will recapture with his rook and White will take that, too; the purpose of Black’s recapture will be to attract White’s queen away from the defense of the bishop on b2. This way after White plays QxR, Black has QxB. White still has gained a bishop and a rook in return for a bishop and a knight, and thus has won the exchange, but it's important to see this side consequence of the idea. The point: account for the defensive work your pieces are doing before you send them off to make attacks.