White is under no menace. He proceeds to attack and selects the QP as his object. The first step is to block it with R-Q4. The QP is pinned, as long as the Black Rook tries to defend it. If Black replies K-B1, White proceeds to assail the pinned and blocked Pawn anew by PQB4. PxP is unplayable because of RxRch. So Black must abandon the Pawn and seek compensation elsewhere, preferably by R-X1, in counterattack upon a weak White pawn.