Here is what St. Thomas Aquinas says about the Eucharist (found in today's Office of Readings):
Since it was the will of God’s only-begotten Son that men should share in his divinity, he assumed our nature in order that by becoming man he might make men gods. Moreover, when he took our flesh he dedicated the whole of its substance to our salvation. He offered his body to God the Father on the altar of the cross as a sacrifice for our reconciliation. He shed his blood for our ransom and purification, so that we might be redeemed from our wretched state of bondage and cleansed from all sin. But to ensure that the memory of so great a gift would abide with us for ever, he left his body as food and his blood as drink for the faithful to consume in the form of bread and wine.
O precious and wonderful banquet, that brings us salvation and contains all sweetness! Could anything be of more intrinsic value? Under the old law it was the flesh of calves and goats that was offered, but here Christ himself, the true God, is set before us as our food. What could be more wonderful than this? No other sacrament has greater healing power; through it sins are purged away, virtues are increased, and the soul is enriched with an abundance of every spiritual gift. It is offered in the Church for the living and the dead, so that what was instituted for the salvation of all may be for the benefit of all. Yet, in the end, no one can fully express the sweetness of this sacrament, in which spiritual delight is tasted at its very source, and in which we renew the memory of that surpassing love for us which Christ revealed in his passion.
It was to impress the vastness of this love more firmly upon the hearts of the faithful that our Lord instituted this sacrament at the Last Supper. As he was on the point of leaving the world to go to the Father, after celebrating the Passover with his disciples, he left it as a perpetual memorial of his passion. It was the fulfilment of ancient figures and the greatest of all his miracles, while for those who were to experience the sorrow of his departure, it was destined to be a unique and abiding consolation.
St. Thomas Aquinas's beautiful hymn, Adoro te devote, expresses these truths poetically (The English translation that follows is from Gerard Manley Hopkins, S.J.):
|Adoro te devote, latens Deitas,|
Quæ sub his figuris vere latitas;
Tibi se cor meum totum subjicit,
Quia te contemplans totum deficit.
|Godhead here in hiding, whom I do adore,|
Masked by these bare shadows, shape and nothing more,
See, Lord, at Thy service low lies here a heart
Lost, all lost in wonder at the God thou art.
|Visus, tactus, gustus in te fallitur,|
Sed auditu solo tuto creditur.
Credo quidquid dixit Dei Filius;
Nil hoc verbo veritátis verius.
|Seeing, touching, tasting are in thee deceived:|
How says trusty hearing? that shall be believed;
What God's Son has told me, take for truth I do;
Truth Himself speaks truly or there's nothing true.
|In cruce latebat sola Deitas,|
At hic latet simul et Humanitas,
Ambo tamen credens atque confitens,
Peto quod petivit latro pœnitens.
|On the cross Thy godhead made no sign to men,|
Here Thy very manhood steals from human ken:
Both are my confession, both are my belief,
And I pray the prayer of the dying thief.
|Plagas, sicut Thomas, non intueor:|
Deum tamen meum te confiteor.
Fac me tibi semper magis credere,
In te spem habere, te diligere.
|I am not like Thomas, wounds I cannot see,|
But can plainly call thee Lord and God as he;
Let me to a deeper faith daily nearer move,
Daily make me harder hope and dearer love.
|O memoriale mortis Domini!|
Panis vivus, vitam præstans homini!
Præsta meæ menti de te vívere,
Et te illi semper dulce sapere.
|O thou our reminder of Christ crucified,|
Living Bread, the life of us for whom he died,
Lend this life to me then: feed and feast my mind,
There be thou the sweetness man was meant to find.
|Pie Pelicane, Jesu Domine,|
Me immundum munda tuo sanguine:
Cujus una stilla salvum facere
Totum mundum quit ab omni scelere.
|Bring the tender tale true of the Pelican;|
Bathe me, Jesu Lord, in what Thy bosom ran
Blood whereof a single drop has power to win
All the world forgiveness of its world of sin.
|Jesu, quem velatum nunc aspicio,|
Oro, fiat illud quod tam sitio:
Ut te revelata cernens facie,
Visu sim beátus tuæ gloriæ. Amen
|Jesu, whom I look at shrouded here below,|
I beseech thee send me what I thirst for so,
Some day to gaze on thee face to face in light
And be blest for ever with Thy glory's sight. Amen.
Incidentally, I just returned from a trip to France, where I visited St. Thomas Aquinas's tomb at the Church of the Jacobins in Toulouse. Here's a picture.