O sacrament most holy

The Holy Eucharist is called the "source and summit" of our Catholic faith, but do we really understand its true meaning?  What is meant by the “Real Presence” of Jesus in the Eucharist, how does this happen, and when did Christians first believe in His words of consecration to be taken literally? Jesus said: “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. Whoever eats my flesh and drinks my blood has eternal life, and I will raise him on the last day. For my flesh is true food, and my blood is true drink.” (Jn 6:53- 55). Recalling these words of Jesus, the Catholic Church professes that, in the celebration of the Eucharist, bread and wine become the Body and Blood of Jesus Christ, through the power of the Holy Spirit and the instrumentality of the priest. The Holy Mass is the sacrifice by which the Church not only remembers Jesus Christ, but really brings Him, His saving Death, and His Resurrection into the present, so we might become part of it.  So, in celebrating the Eucharist, Jesus is truly there. By his Real Presence in the Eucharist, Christ fulfils his promise to be with us "always, until the end of the age" (Mt 28:20).  In the Eucharist, the Church both receives the gift of Jesus Christ and gives grateful thanks to God for such a blessing.  This thanksgiving is the only proper response, for through this gift of Himself in the celebration of the Eucharist, under the appearances of bread and wine, Christ gives us the gift of eternal life.