While waiting for Dumbledore in his office, Harry discovers a Pensieve, which holds Dumbledore's memories:
Why did the Pensieve reveal itself to Harry Potter?
While waiting for Dumbledore in his office, Harry discovers a Pensieve, which holds Dumbledore's memories:
Why did the Pensieve reveal itself to Harry Potter?
The pompous effect of the door opening itself to present the Pensieve as magnificent magical object is only in the movie. It was probably included to add some drama to the scene.
In the book Harry noticed the glow through the door ajar by accident and he got so curious to open the door and examine the source of light.
The sword had once belonged to Godric Gryffindor, founder of Harry's House. He was gazing at it, remembering how it had come to his aid when he had thought all hope was lost, when he noticed a patch of silvery light, dancing and shimmering on the glass case. He looked around for the source of the light and saw a sliver of silver-white shining brightly from within a black cabinet behind him, whose door had not been closed properly. Harry hesitated, glanced at Fawkes, then got up, walked across the office, and pulled open the cabinet door.
Indeed later Dumbledore confirmed he had been in a hurry and might have left his cabinet half-open:
"I was using the Pensieve when Mr. Fudge arrived for our meeting and put it away rather hastily. Undoubtedly I did not fasten the cabinet door properly. Naturally, it would have attracted your attention."
I'm quite sure that Dumbledore wanted Harry to discover the Pensieve.
In the book the accident of leaving the door slightly ajar was on purpose.
In the movie, he would have enchanted the cabinet to dramatically open while Harry was in his office.