Hula!
Right after those words were spoken, a jade token flew forth from Jiang Fangyou's palm. It floated out of the window of the treasure vault, and the next moment, the surroundings seemed to suddenly come to life. An overwhelming aura suddenly shrouded the entire area.
With Jiang Fangyou's eye of discernment, he could tell that the treasures had not been taken too long ago. With a swift calculation, he deduced that it was likely that the thief had not managed to escape from the treasure vault yet.
As long as he sealed the area with the formation and combed the entire treasure vault carefully, he would surely be able to weed that darned thief out!
After sealing the area, the two of them moved on to the third floor. Seeing that the third floor had been emptied as well, Jiang Fangyou's eyebrows twitched in trepidation. His chest felt so stifled that it seemed as if it would blow up very soon.
The idea of 'containing fortune' might seem a little abstract, but it's a Chinese geomancy (Fengshui) concept. Luck is viewed as a force existent in this world, embedded into the environment.
These environments would be called 'auspicious', or more often in this book, 'blessed lands'. However, as the environment is constantly changing, luck would often move around with time. In other words, no matter how auspicious a land is, luck will eventually leave the land, thus possibly causing the gradual decline of a clan or power residing in the area. As such, there are powerful artifacts used to 'seal or contain the luck' within the area so as to prevent it from leaving.
This is just a really simplified explanation just to give a brief idea about what the concept means, so do take it with a pinch of salt.