If you have a bishop bearing down on the long diagonal leading into the king’s corner, you may not need to get your queen or rook onto h8; if the g-file is open (as distinct from the g-pawn merely being advanced), you can use a heavy piece to seal off the file from a distance, with mate then resulting because the king is attacked and cannot move. In the diagram to the left, where Black is mated, the king can be on g8 or h8 and the mate works either way; but notice that if the king is on h8 White does have a problem to worry about: Black can interpose a pawn on f6, interrupting the White bishop’s path and doing it with protection from the rook on f8. We will look further at this complication later. For convenience let us oversimplify and refer to this pattern as Morphy’s mate, though that term technically refers to one particular way of reaching this position that we will examine in a moment.
Notice the relationship between this pattern and the previous one. The idea there was to use a bishop to attack a square (h8) and then also plant a heavy piece on it. Here the idea is to let the heavy piece do its work from a distance. From so far away it still can take care of g8 as a flight square, as shown here. The rook can't attack h7 as it could if it were sitting on h8; but in this case Black's own pawn seals off the square.