If you really understand a true Catholic you would understand that the beliefs of a Catholic is based on a 3 leg stool. Bible, Tradition, and Magisterium. If you ever read the Nicene creed you will understand that just like other Christians, Catholics are believers in Christ and believe in salvation (see below), the church isn't my salvation Jesus is and always been since I baptized as an infant. I believe in my salvation and attend both Catholic and Evangelical Churches. I believe in the Body and Blood of Christ, Communion of Saints, and life everlasting. I detest the false knowledge spilled, and hope to spread peace. True Christians except other Christian beliefs, and understand that as human we cannot understand the full scope of God's will, only his moral will is revealed in the bible. It's is in study with those who believe differently that we learn and grow together. Catholics are Justified through Grace and are infused by it. Read this article about Catholics & Protestants.
I believe that most protestants have a false idea about the Mass and where it comes from. If you look back to Exodus you will see Exodus 32 they eat of the goat. If you understand later in Leviticus you will see a sacrifice for sin offerings. Then If you understand Covenant theology, That those sacrifices were done to keep the covenant with God. If you study the Jewish word for Covenant, you would learn that it is a family bond or marriage agreement (to create communion). Jesus in passover made himself the passover lamb and made himself offering up for sin. One sacrifice for all. He took the "Cup of blessing (Jewish 3 cup in passover) and made a Covenant with humanity. If you read John 6:53-57 you would see that he says, "Jesus said to them, "I tell you the truth, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you. 54 Whoever eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day. 55 For my flesh is real food and my blood is real 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 live because of the Father, so the one who feeds on me will live because of me."
If you believe in the sacrifice of Jesus, you would say that it is"eternal", and because the sacrifice is eternal the communion offering from holy Thursday is eternal as well. Thus, why Paul speaks about Communion in Corinthians.
We believe in one God,
the Father, the Almighty,
maker of heaven and earth,
of all that is, seen and unseen.
We believe in one Lord, Jesus Christ,
the only Son of God,
eternally begotten of the Father,
God from God, light from light,
true God from true God,
begotten, not made,
of one Being with the Father;
through him all things were made.
For us and for our salvation
he came down from heaven,
was incarnate of the Holy Spirit and the Virgin Mary
and became truly human.
For our sake he was crucified under Pontius Pilate;
he suffered death and was buried.
On the third day he rose again
in accordance with the Scriptures;
he ascended into heaven
and is seated at the right hand of the Father.
He will come again in glory to judge the living and the dead,
and his kingdom will have no end.
We believe in the Holy Spirit, the Lord, the giver of life,
who proceeds from the Father [and the Son],
who with the Father and the Son is worshiped and glorified,
who has spoken through the prophets.
We believe in one holy catholic and apostolic Church.
We acknowledge one baptism for the forgiveness of sins.
We look for the resurrection of the dead,
and the life of the world to come. Amen.