What interesting visual pattern do you see here? Black pieces lined up on the seventh rank. The White rook on e1 is poised to attack at e7, but Black's queen prevents this and isn’t a feasible target anyway since it can bite (true, it is pinned by White's queen, so it can't "bite" the rook; but since 1. Re7 doesn't give check, Black can reply to it with 1. ...QxQ). Still, the idea suggested by the arrangement of Black’s pieces is the important thing because it guides your thought experiments: now you have in mind an attack with the rook and can look for exchanges or other forcing moves that might make it possible, particularly by replacing the queen with a better target. White has a capture (and check) available for the purpose: QxQ+, to which Black replies KxQ. Now comes White's Re7+, forking and winning the now-loose bishop on f7.