The form and the formless are chasing each other and trying to catch each other. It's a chase without an end because both are moving in the same speed. They are dependent on each other. The form cannot exist without the formless and the formless cannot exist without the form. If they would stop chasing each other and be still, they would be ripped apart by the fierce vortex which they have created in their chase. They would pop like a bubble and dissolve into thousand pieces and that's what they're the most afraid of...