St. Thomas Aquinas (teaching, not singing) on the holy Eucharist: from 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.