When speaking of two natures unified in Christ, the reference cannot be to universal natures, because universal natures apply to the Father and the Spirit equally — which would entail that the Father and Spirit also became man.
In Christian theology, the Holy Spirit, understood as the third person of the Trinity—often described as God's active presence or power in the world.
Two natures unified in Christ(Christian theology)
A Christian theological idea that Jesus Christ is both fully divine (God's nature) and fully human (human nature) existing together in one person.
Universal natures(theology and metaphysics)
Qualities or essences that apply to all members of a group in the same way—like how all dogs share the universal nature of 'being a dog.' In this context, it means characteristics that would be true of God the Father, God the Son, and God the Holy Spirit equally.
In Arbiter (Arbitrator or Umpire), written about the same time as the Council of Constantinople and surviving only in Syriac translation, Philoponus takes the view that the locution ‘discernible in two natures’ ought to be abandoned. His main strategy is to argue that in this context the meaning of the terms ‘nature’ and ‘hypóstasis’ are essentially identical, so that if Christ is (according to (3)) one hypóstasis he cannot also (as in (4)) be discernible in two natures. The argument goes roughl