This was intended to combat both Nestorius's two-persons approach and the monophysite doctrine of Jesus as being so divine that his humanity was overwhelmed. This allowed the Church to affirm that Jesus was truly one person who both participated in the divine Trinitarian "economy" as well as in the human sphere of material being.
This was intended to counter both Nestorius's dualistic Christology and the monophysite doctrine, which held that Jesus' humanity was absorbed by his divinity. This enabled the Church to affirm Jesus' unity as one person who participated in both the divine Trinitarian economy and the human realm of material existence.