The early Church which canonized the Bible did so in light of the teachings of the early Church led by the Apostles. They chose the writings as inspired by comparing them to the Tradition handed on by the Apostles.
1324 The Eucharist is “the source and summit of the Christian life.”136 “The other sacraments, and indeed all ecclesiastical ministries and works of the apostolate, are bound up with the Eucharist and are oriented toward it. For in the blessed Eucharist is contained the whole spiritual good of the Church, namely Christ himself, our Pasch.”137
1325 “The Eucharist is the efficacious sign and sublime cause of that communion in the divine life and that unity of the People of God by which the Church is kept in being. It is the culmination both of God’s action sanctifying the world in Christ and of the worship men offer to Christ and through him to the Father in the Holy Spirit.”138
1326 Finally, by the Eucharistic celebration we already unite ourselves with the heavenly liturgy and anticipate eternal life, when God will be all in all.139
1327 In brief, the Eucharist is the sum and summary of our faith: “Our way of thinking is attuned to the Eucharist, and the Eucharist in turn confirms our way of thinking.”
I,m borrowing this from an EWTN Article written by Jim Dobbins .It really captures this well
http://www.ewtn.com/library/SPIRIT/ITEFFECT.TXT
If the Eucharist is a sacrament of Love, it is necessarily a sacrament of union. As Boylan says (1), “All love demands union; the more ardent the love, the more complete the union it seeks.
The love of our Lord for us is no exception.” It is through the operation of the Eucharist that He brings us to union with Himself, and it is through the Eucharist that He communicates to us His Divine Life, His Divine nature. We see this desire for union in the married state. The greater the love, the greater the desire for union, and in the union there springs forth life. So, too, with God. The married state is a prefigure of the union we
anticipate with God. St. Paul, in 1 Cor 6:16, calls marriage the symbol and shadow of the still more intimate union of Christ with
His Church. Since we are His Church, the Mystical Body, it is a union of God with us that St. Paul refers, or rather a union of us with God. If we look at the prayer of Jesus at the Last Supper, as told by St. John, when Jesus instituted the Eucharist, it is a prayer of union. It is no coincidence that Our Lord gave us this
prayer at the very ceremony at which He gave us the means to effect this union.
We also see that Our Lord has continued His love of contradiction with the Eucharist. When He chose His disciples, He told them they
would be fishers of men. These fishermen knew well that when they fish, the fish are alive and, when caught, they die. When they fish for men, the men are spiritually dead, and in being caught they receive eternal Life. In the Eucharist we have a similar contradiction. Ordinary food is consumed and becomes that which consumes it. In the Eucharist, we consume God and become that which we consume.
Jesus did not merely become one of us, suffer human hardship, and die for us. He loves us with such a complete and infinite love that He wants us completely united with Him. He wants to give of Himself to us over and over through the Eucharist so that more and more we may share in Him; that more and more, as Jesus said(2), “... they may all be one; even as You, Father, are in Me, and I in
You, that they also may be in Us, ... . The glory which You have given Me I have given to them, that they may be one even as We are One.” To do this, He provided us with this most perfect means of unity; the Eucharist.
This infinite Gift, this Most Perfect of all possible gifts, comes to us in the most humble way possible. Through the action of the priest, simple unleaven bread, and simple wine, each become the Body and Blood, Soul and Divinity of the living and triumphant Jesus Christ, the same Jesus Christ Who defeated satan and conquered death. Through the action of the priest, Jesus has given us this most profound sacrament, this most unimposing means to share in His Divine Life, this most astonishing gift of Himself as
our most precious of all possible foods. He has given us the ultimate gift of His Love. There is nothing else in all of creation that can compare with this gift. It is Divinely unique.
Not only has Our Lord given us this gift of the Eucharist, He has told us, in this prayer at the Last Supper, the effects of the Eucharist. It is stated in such simple terms, and yet has such profound meaning. We shall abide in Him, and He shall abide in us.
We shall be united with Jesus in the most intimate of all possible ways. He shall give us His Life, just as His Life was given to Him by the Father.
“Material food first changes into the one who eats it, and then, as a consequence, restores to him lost strength and increases his vitality. Spiritual food, on the other hand, changes the person who eats it into itself. Thus the effect proper to this Sacrament is the conversion of a man into Christ, so that he may no longer live, but Christ lives in him; consequently, it has the double effect of restoring the spiritual strength he had lost by his sins and defects, and of increasing the strength of his virtues.” St. Thomas, Commentary on Book IV of the Sentences, d.12, q.2, a.11