Things happen and do not happen at the same time. Although The Heart Sutra seems to emphasize the side of things not happening (“neither arises nor perishes…neither increases nor decreases”), we also need to understand and see through to the side of things happening. Movements for war and peace are constantly taking place, and we are called to choose one over the other every moment of every day.
The Heart Sutra claims that in the midst of phenomena where all things are changing, the reality of boundless interactions continues, and that this fact itself will not change. After all, the ultimate reality both encompasses and is free of change in all manifestations.
From The Heart Sutra: A Comprehensive Guide to the Classic of Mahayana Buddhism by Kazuaki Tanahashi, page 12