This interesting question speaks to the physics as well as the chemistry of digestion. It simply isn't enough to dump chemicals into something to get a reaction. We must mix or agitate the ingredients to optimize the effect. That physical process is an aid to the chemistry involved.
Peristalsis is the movement of the involuntary muscles that provide the motive force in the digestive tract. With this action, we see the contents of the system "churned" in a way that serves to mix the digestive enzymes and the food together, as well as expose different parts of the mix to the walls of the intestines so that absorption and uptake can occur. Think this one through as you scan other information that you access using the links below.