The same idea in slightly different visual form. White's bishop and rook on the d-file, of course, create a possible discovery against Black’s loose bishop. To unleash it White needs a violent and distracting move for his own bishop to make. As the piece can't give check or make a good capture, White looks for threats the bishop can make and sees that it can attack the rook on b6. There are two ways to do it: Bc5 or Bc7. Which is better?

Answer: Bc7 is better. In reply to Bc5 Black could play Rb7, both moving the rook to safety and using it to protect the bishop on d7. Bc7 not only threatens Black’s rook and bishop at the same time, but also makes Rb7 an ineffective reply. White wins the bishop. Notice the general point, though: you always want to be mindful of any way the enemy might be able to move the target and address your other threat in one stroke.