Look for pieces aimed toward White's king and you find Black's battery of queen and bishop on the long light-squared diagonal, threatening to mate on g2. White defends against the threat with his queen. Again, what you also must see is that White’s king is trapped on the back rank, nearly able to be mated with Re1—another possibility thwarted only by White’s queen. Re1+ thus makes White’s position untenable, just as a similar rook move did in the last position. If White takes the rook with his queen, Black mates on g2; if he takes the rook with his knight, Black mates on h1.