The only begotten Son of God, wishing to enable us to share in his divinity, assumed our nature, so that by becoming man he might make us gods.
Moreover, he turned the whole of our nature, which he assumed, to our salvation. For he offered his body to God the Father on the altar of the cross as a sacrifice for our reconciliation; and he shed his blood for our ransom and our cleansing, so that we might be redeemed from wretched captivity and cleansed from all sins.
Now in order that we might always keep the memory of this great act of love, he left his body as food and his blood as drink, to be received by the faithful under the appearances of bread and wine.
How precious and how wonderful is this banquet, which brings us salvation and is full of all delight! What could be more precious? It is not the meat of calves or kids that is offered, as happened under the Old Law; at this meal Christ, the true God, is set before us for us to eat. What could be more wonderful than this sacrament?
No sacrament contributes more to our salvation than this; for it purges away our sins, increases our virtues, and nourishes our minds with an abundance of all spiritual gifts.
It is offered in the Church for the living and the dead, so that it may be beneficial to all, as it was instituted for the salvation of all.
Finally, no one is capable of expressing the delight of this sacrament, through which the sweetness of the Spirit is tasted at its source, and the memory is celebrated of that surpassing love which Christ showed in his passion.
And so, in order to imprint the immensity of this love more deeply in the hearts of the faithful, at the Last Supper, when the Lord had celebrated the Pasch with his disciples and was about to pass from this world to his Father, he instituted this sacrament as a perpetual memorial of his passion. It fulfilled the types of the Old Law; it was the greatest of the miracles he worked; and he left it as a unique consolation to those who were desolate at his departure.
This reading is from the works of St Thomas Aquinas OPUS 57,1-4