St. Justin Martyr described the Eucharistic Liturgy in 155 AD in his First Apology.The Paschal mystery of Christ is celebrated in the liturgy of the Mass.
The Mass (or Divine Liturgy in the East) is the Eucharist or principal sacramental celebration of the Church, established by Jesus at the Last Supper, in which the mystery of our salvation through participation in the sacrificial death and glorious resurrection of Christ is renewed and accomplished.
The word “Mass” comes from the Latin missa, as it refers to the mission or sending forth of the faithful following the celebration, so that they may fulfill God’s will in their daily lives.
The essential signs of the sacrament are wheat bread and grape wine, on which the blessing of the Holy Spirit is invoked during the Sacrifice of the Mass, and the priest pronounces the words of consecration spoken by Jesus at the Last Supper: “This is my body…This is the cup of my blood…” (Matthew 26:26-28, Mark 14:22-24, 1 Corinthians 11:23-26).
Jesus died once on the cross in sacrifice for our sins (Hebrews 9:25-28). But Jesus is present for all time, as he is the eternal Son of God. What he did once in history also then exists for all eternity. What happened in time goes beyond time. In the heart of Jesus he is always giving himself to the Father for us, as he did on the Cross. When we celebrate the Mass, the sacrifice of the cross, that happened once in history but is present for all eternity, that same reality is made present in mystery.1
The bread and wine through Transubstantiation become the Body and Blood, Soul and Divinity of Jesus Christ, and we receive the Real Presence of Jesus when we receive Holy Communion. Our soul is nourished, helping us to become like Christ. The Eucharist is the heart and source of community within the Church. Receiving Holy Communion with others during the Mass brings unity of the Church, the Body of Christ (I Corinthians 10:16-17).
Then he took the bread, said the blessing,
broke it, and gave it to them, saying,
“This is my body, which will be given for you;
do this in memory of me.”
And likewise the cup after they had eaten, saying,
“This cup is the new covenant in my blood, which will be shed for you.”
Gospel of Luke 22:19-20