Why does the Torah mention Shabbos immediately before listing all of the festivals?
There are two fundamental ideas that make up emunah. First, we believe that G-d created the world—that everything originally came into existence because G-d brought it into being. But there is a second step: believing that G-d continues to run the world and is involved in everything that happens.
Shabbos reminds us that G-d created the world. Every week, we stop creating and working and recognize that the world belongs to its Creator.
The festivals, on the other hand, commemorate the miracles of the Exodus. They remind us that G-d doesn't simply create the world and then step away. He continues to control nature and guide events according to His will.
By placing Shabbos together with the festivals, the Torah teaches us that both ideas are essential. G-d is not only the Creator—He is also the Sustainer.
Emunah means recognizing that G-d is present not only in the beginning of creation, but in every moment of our lives.