From this opening statement, the crescendo grows stronger moving to how God provided for the Children of Israel in the desert:
Notice that through out the chapter Jesus has been dealing with physical food; feeding people, referring to himself as bread, then recalling how the Children of Israel had been physically fed in the desert. Beginning in v. 51 and moving forward, Jesus now with no doubt reveals himself as the new Lamb of the Passover. Just as the Children of Israel had to consume the Lamb, Christ himself now had to be consumed, physically:
I am the living bread that came down from heaven; whoever eats this bread will live forever; and the bread that I will give is my flesh for the life of the world." 52 The Jews quarreled among themselves, saying, "How can this man give us (his) flesh to eat?" 53 Jesus said to them, "Amen, amen, I say to you, unless you eat the flesh of the Son of Man and drink his blood, you do not have life within you. 54 Whoever eats my flesh and drinks my blood has eternal life, and I will raise him on the last day. 55 For my flesh is true food, and my blood is true drink. 56 Whoever eats my flesh and drinks my blood remains in me and I in him. 57 Just as the living Father sent me and I have life because of the Father, so also the one who feeds on me will have life because of me. 58 This is the bread that came down from heaven. Unlike your ancestors who ate and still died, whoever eats this bread will live forever."
Wow. This was extremely offensive to the Jews that were in Capernaum listening to Christ. Eating human flesh was a sacrilege to them, yet the words that Christ used in this were the same words used for the consumption of the bread in the desert. Christ was not using symbolism or hyperbole in this. He was telling us that as sin came into the human race through the consumption of fruit, our redemption would now come through the consumption of his Flesh and Blood. If at this point you feel the hair standing up on the back of your neck, and you are offended at the thought of this, you are probably feeling the same thing that some of Christ's disciples felt:
60 Then many of his disciples who were listening said, "This saying is hard; who can accept it?"
61 Since Jesus knew that his disciples were murmuring about this, he said to them, "Does this shock you? 62 What if you were to see the Son of Man ascending to where he was before? 63 It is the spirit that gives life, while the flesh is of no avail. The words I have spoken to you are spirit and life. 64 But there are some of you who do not believe." Jesus knew from the beginning the ones who would not believe and the one who would betray him. 65 And he said, "For this reason I have told you that no one can come to me unless it is granted him by my Father." 66 As a result of this, many (of) his disciples returned to their former way of life and no longer accompanied him.
The cup of blessing that we bless, is it not a participation in the blood of Christ? The bread that we break, is it not a participation in the body of Christ?
24 and, after he had given thanks, broke it and said, "This is my body that is for you. Do this in remembrance of me." 25 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." 26 For as often as you eat this bread and drink the cup, you proclaim the death of the Lord until he comes. 27 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. 28 A person should examine himself, and so eat the bread and drink the cup. 29 For anyone who eats and drinks without discerning the body, eats and drinks judgment on himself.
"Take note of those who hold heterodox opinions on the grace of Jesus Christ which has come to us, and see how contrary their opinions are to the mind of God..."They abstain from the Eucharist and from prayer because they do not confess that the Eucharist is the flesh of our Savior Jesus Christ, flesh which suffered for our sins and which that Father, in his goodness, raised up again. They who deny the gift of God are perishing in their disputes" (Epistle to the Smyrnaeans 6:2; 7:1 [A.D. 110]).
"We call this food Eucharist, and no one else is permitted to partake of it, except one who believes our teaching to be true and who has been washed in the washing which is for the remission of sins and for regeneration [baptism] and is thereby living as Christ enjoined."For not as common bread nor common drink do we receive these; but since Jesus Christ our Savior was made incarnate by the word of God and had both flesh and blood for our salvation, so too, as we have been taught, the food which has been made into the Eucharist by the Eucharistic prayer set down by him, and by the change of which our blood and flesh is nurtured, is both the flesh and the blood of that incarnated Jesus" (First Apology 66:1-20 [A.D. 148]).
"He has declared the cup, a part of creation, to be his own blood, from which he causes our blood to flow; and the bread, a part of creation, he has established as his own body, from which he gives increase unto our bodies."When, therefore, the mixed cup [wine and water] and the baked bread receives the Word of God and becomes the Eucharist, the body of Christ, and from these the substance of our flesh is increased and supported, how can they say that the flesh is not capable of receiving the gift of God, which is eternal life--flesh which is nourished by the body and blood of the Lord, and is in fact a member of him?" (Against Heresies 5:2 [A.D. 148]).
26 The Advocate, the holy Spirit that the Father will send in my name--he will teach you everything and remind you of all that (I) told you.
But this one offered one sacrifice for sins, and took his seat forever at the right hand of God
I think that it was at this time that I realized that the greatest gift that our Lord left us was Himself. In the Mass Catholics all around the world are focused on the center of our Faith and our Salvation, the Sacrifice of our Lord. Inspiring messages are great and necessary (St. Jerome said that ignorance of Scripture is ignorance of Christ), but that is not what Christ left us. The greates thing that Christ left us was himself. We were promised that Christ would never leave us or forsake us and with the Sacrament of Holy Communion, he has fulfilled that. Everytime we celebrate the Sacrifice of the Mass we once again are given the opportunity to come into complete communion with Our Lord and receive all the graces that entails. And even more than that, the Sacrifice is being continually lifted up before God thousands upon thousands of times a day from altars around the world.