Eucharist And Unity

Sed Dominus nihil fidelium conscientiae incertum relinquens, ipsum illum naturalis efficientiae docuit effectum, dicens, Ut sint unum, sicut nos unum sumus, ego in his, et tu in me; ut sint perfecti in unum. Eos nunc, qui inter Patrem et Filium voluntatis ingerunt unitatem, interrogo utrumne per naturae veritatem hodie Christus in nobis sit, an per concordiam voluntatis? Si enim vere Verbum caro factum est, et vere nos Verbum carnem cibo dominico sumimus; quomodo non naturaliter manere in nobis existimandus est, qui et naturam carnis nostrae jam inseparabilem sibi homo natus assumpsit, et naturam carnis suae ad naturam aeternitatis sub sacramento nobis communicandae carnis admiscuit? Ita enim omnes unum sumus, quia et in Christo Pater est, et Christus in nobis est. Quisquis ergo naturaliter Patrem in Christo negabit, neget prius non naturaliter vel se in Christo, vel Christum sibi inesse; quia in Christo Pater, et Christus in nobis, unum in his esse nos faciunt. Si vere igitur carnem corporis nostri Christus assumpsit, et vere homo ille, qui ex Maria natus fuit, Christus est, nosque vere sub mysterio carnem corporis sui sumimus, et per hoc unum erimus, quia Pater in eo est, et ille in nobis; quomodo voluntatis unitas asseritur, cum naturalis per sacramentum proprietas, perfectae sacramentum sit unitatis. Non est humano aut saeculi sensu in Dei rebus loquendum: neque per violentam atque imprudentem praedicationem; coelestium dictorum sanitati, alienae atque impiae intelligentiae extorquenda perversitas est. Quae scripta sunt legamus, et quae legerimus intelligamus: et tum perfectae fidei officio fungemur. De naturali enim in nobis Christi veritate quae dicimus, nisi ab eo didicimus, stulte atque impie dicimus. Ipse enim ait, Caro mea vere est esca, et sanguis meus vere est potus. Qui edit carnem meam, et bibit sanguinem meum, in me manet, et ego in eo. De veritate carnis et sanguinis non relictus est ambigendi locus. Nunc enim et ipsius Domini professione, et fide nostra vere caro est, et vere sanguis est. Et haec accepta atque hausta id efficiunt, ut et nos in Christo, et Christus in nobis sit. Anne hoc veritas non est? Contingat plane his verum non esse, qui Christum Jesum verum esse Deum denegant. Sanctus Hilarius Pictaviensis, De Trinitate, Lib VIII Source: Migne PL 10.245b-247b

But the Lord leaves no doubt in the minds of the faithful, He has taught the effect of the operation of His nature , saying, 'That they may be one, as we are one, I in them and you in me, that they may be perfected in one.' 1 Now I ask those who bring forward a unity of will between the Father and the Son, whether Christ is in us today by truth of nature or by agreement of will. For if truly the Word has been made flesh and we truly receive the Word made flesh as food from the Lord, must we not believe that He abides in us naturally, He who, born as a man, took up the nature of our flesh now inseparable from Himself, and has joined the nature of His own flesh to the nature of the eternal Godhead in the sacrament by which His flesh is communicated to us? So we are all one, because the Father is in Christ and Christ is in us. Whoever then shall deny that the Father is in Christ naturally must first deny that either he is naturally in Christ or Christ in him, because the Father in Christ and Christ in us make us one in them. Therefore if Christ truly took to Himself the flesh of our body, and truly that man who was born from Mary is Christ, and we truly receive in a mystery the flesh of His body, and by this we shall be one, because the Father is in Him and He in us, how is a unity of will asserted when the property of nature received through the sacrament is the sacrament of perfect unity? One must not speak of the things of God in a human or worldly sense, nor by a violent and foolish preaching must an impious and perverse understanding be extorted from the soundness of the heavenly words. Let us read what has been written, let us understand what we read, and then fulfil the duties of perfect faith. Now concerning what we say about the truth of Christ's nature within us, unless we have been taught by Him, we speak foolishly and impiously. For He Himself says, 'My flesh is meat indeed and my blood is drink indeed. He who eats my flesh and drinks my blood abides in me and I in him.' 2 Regarding the truth of the flesh and blood there is no room left for doubt. For now by both the proclamation of the Lord Himself and our own faith it is true flesh and true blood. And these eaten and drunk make it so that both we are in Christ and Christ in us. Is this not the truth? Certainly it may happen that these things are not true to those who deny that Christ Jesus is truly God. Saint Hilary of Poitiers, On The Trinity, Book 8 1 Jn 17.22-23 2 Jn 6.55-56