For the Chalcedonians, the hypostatic union was the center of Jesus's unity (his divinity and humanity being described as natures) whereas those who rejected the Chalcedonian definition saw his nature as the point of unity.
The hypostatic union served as the core of the Chalcedonians' concept of Jesus' oneness, distinguishing between his divine and human aspects as distinct natures. Conversely, those who opposed the Chalcedonian stance saw his essence as the unifying factor.