To introduce this article, I will let Saint Paul instruct us, with his first letter to the Corinthians chapter 11, verses 23-27, where he says “For I received from the Lord what I also handed down to you, that the Lord Jesus, on the night that He was handed over, took bread, and, after He had given thanks, broke it and said ‘This is My body that is for you. Do this in remembrance of Me.’ In the same way also the cup, after supper saying, ‘This cup is the new covenant in My blood. Do this, as often as you drink it, in remembrance of Me.’ For as often as you eat the bread and you drink the cup, you proclaim the death of the Lord until He comes. Therefore, whoever eats the bread or drinks the cup of the Lord unworthily will have to answer for the body and blood of the Lord.”

Notice that Saint Paul reports the words of Jesus as “This is My body,” and not, “This represents my body;” and similarly for the blood. Another version of the words used is also seen in the Holy Gospel according to Saint Matthew the Apostle, chapter 26, verses 26 to 28, and also in the Gospels according to Saint Mark and Saint Luke.

Thus, it can now be seen that one can truly eat the body and drink the blood of Christ under the appearances of bread and wine. Jesus had warned His disciples that the day would come when they would be doing just that, as recorded in the Holy Gospel according to Saint John the Apostle, chapter 6, verses 53-57, after which many disciples left Him, not able to stomach His words, not having sufficient faith in Jesus such that He would find a way to accomplish this prophecy.

Therein is the essence of the Mass. Therein comes the Catholic Doctrine of the "Real Presence of Our Lord Jesus Christ" in the Holy Eucharist. Every prayer and ceremonial leading up to the Consecration of the species is a preparation for the re-enactment of the death of Jesus Christ on the Cross, but in an unblody way.

The Roman Catholic Mass is the universal prayer of the Church and of all of the followers of Christ in the Roman Catholic Church. It is composed of many parts, or movements, something like a concert. It has a unique structure and message whose presentation is the subject of the following sections.