The Containment's purpose is to preserve the most important thing and tend to them and keep them away from harm. Whenever it needs more space to preserve more things, it will grow itself by consuming other things such as a planet or a star. When no other things are able to be consumed when it needs to grow, it will shrink the objects inside it. Currently, it has managed to preserve a Multiverse and an Earth. It has consumed 3 galaxies to grow. The walls are extremely hard, but they can be broken. To make up for this, the Containment can repair itself using the material it stores from leftovers or by consuming more less-important objects. The Containment has been theorized to be sentient, but there is very little evidence that it is sentient and is just programmed to function this way.
P.S: Feel free to add more things The Containment preserved
Preserved objects: A Multiverse, Earth, Soup Recipe.