Why do Mall entrances have two sets of doors?

Question

You open one door, then there is a room, then you open the next door and then you are in the store.

Answer 1

It keeps the outside air and inside air from mixing too much....basically it's to take load off the heating and cooling units; and helps to keep temperatures inside the mall fairly uniform.

Answer 2

To keep the inside cool in the summer and warm in the winter without having to heat/cool the building excessively. This saves energy and money at the same time. It also makes it so that the people shopping and working near the entrances are more comfortable. It's called an "air lock."