On Q4, where the Black QP stands, attack and defence are in balance. To obtain the superiority White forces the protecting piece, the Black King, from the scene of action. To this end he uses his "Passed Pawn," the RP. By advancing it, he threatens to Queen it within five moves. Evidently, the Black King must stop that dangerous Pawn. By the sacrifice of the Passed Pawn the White King will be enabled to gain the QP, then the KP and will finally guide his BP to the eighth row, to victory. Therefore, the game proceeds
1 P-R4
K-K3;
2 P-R5
K-Q3;
3 P-R6
K-B3;
4 P-R7
K-Kt2;
5 KxP
KxP;
6 KxP and wins by superiority.