Both queens are under attack; RxQ doesn’t work for Black, as it is met with NxQ (and then the knight guards e1). But meanwhile the convergence of Black’s queen and bishop on g2 obviously suggests an attack on that square with Qg2+, but then White has QxQ. Don’t give up with that observation, however; notice what pattern it leaves behind and think from there. Suddenly (a) White’s king is stuck on the back rank and (b) Black’s rook at e8 has an unobstructed path to e1. Play it through: Re1+ has to be met with Qf1; and now Black mates with RxQ, with his bishop on h3 providing cover for the rook that delivers the mate. From the outset of this position the bishop’s ability to support an attack on g2 is obvious; less obvious, but important, is its ability to support mate with a heavy piece on f1.