Rebuttal: we refuse to turn away from any of Jesus's teachings, regardless of how hard they are to understand. that's what 'faith' is all about!

What the Bible Says

• 1 Timothy 3:15 – "But if I should be delayed, you should know how to behave in the household of God, which is the church of the living God, the pillar and foundation of truth."
  • Whichever 'Church' is doing the action mentioned above IS the Church Jesus started the - One, Holy, Catholic, Apostolic Church. The Church with the true and divine interpretation of God's word handed down through oral tradition and later through written tradition.
• John 20:21 - "[Jesus] said to them again, “Peace be with you. As the Father has sent me, so I send you." And when he had said this, he breathed on them and said to them, “Receive the holy Spirit."
  • God chose the Israelites to establish a covenant with them. He gradually gave his people instructions in preparation for a figure, representing the new and perfect covenant, which was to be ratified in Christ! The New Covenant, in his blood, called together a race made up of Jews and Gentiles which would become one body - not according to the flesh, but according to the Spirit.
• Luke 22:19-20 – "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."'
  • The Eucharist not only a ritual we Catholics partake in, it’s a command from our Lord! It is the Blessed Sacrament of the altar, (Eucharist) to do this in memory of him, proclaiming his death to be our gateway to salvation. Jesus becomes part of us in an infinitely intimate and unique way. It is the most beautiful relationship we are called to be a part of - our physical and spiritual participation in and through the Body of Jesus Christ.
    

In Other Words
The Greek word mysterion was translated into Latin by two terms: mysterium and sacramentum. In later usage the term sacramentum emphasized the visible sign of the hidden reality of salvation which was indicated by the term mysterium. Saint Augustine said, “For there is no other mystery of God, except Christ.”

“How is the Catholic’s discernment differing from a Protestant's discernment?
The difference is in who we believe has the full truth of the gospels. This begs the question of infallibility. The Protestant, in their quest to have a personal private relationship with Jesus, become isolated and the truth of the gospels become whatever they say it is. In a Protestant's mind he / she are infallible, relying on their own intellect, will and judgement. These are all based on his / her own personalities, education, background and other personal characteristics. So, are Protestants suggesting that they are perfectly enlightened? Yes! This is why Protestants often change their traditions or interpretations over time - they realize the error of their ways. This is the problem with "Faith alone and nothing else," which coincides with "Once saved always saved."

For Catholics, the discernment of the truth was deposited onto the apostles.  You can clearly read in the Bible, Jesus established his Church, in order to hand down teachings a guide his believers in truth. The Catholic Bible reader can rest assured that the true deposit of faith and interpretation lies within the infallibility of the Church's head - Peter. Peter was protected by the Holy Spirit to lead Jesus’s Church in the fullness of truth. Peter then deposited this truth to his successors, the popes. A Catholic’s judgement is not his / her own, but a progression of growth within the twelve original ambassadors appointed by Jesus. Therefore a Catholic can be confident that divine revelation, is not of human opinion, but of sound doctrine.

The biblical description of faith in Hebrews 11 is, “...realization of what is hoped for and the evidence of things not seen."  So what is it that we hope for?  Hope here is a reality. The reality of what the Father has provided for us - salvation through Jesus Christ.  This realization comes to us through grace, God’s first move.  Realizing this is objectively true, we exercise our free will to accept or deny this truth.  If you lose hope, you will lose faith. It is impossible to live a righteous life for God without it.  Because I have said "yes" to accept God's grace, more grace is provided through baptism and the other sacraments.

What the Church Teaches

• CCC 889-890: As Christians we understand the difference between divine revelations and mere human opinion. God divinely protects the Catholic Church from authoritatively teaching anything that is false. 
• CCC 781: “At all times and in every race, anyone who fears God and does what is right has been acceptable to him. He has however, willed to make men holy and save them, not as individuals without any bond or link (religion) between them, but rather to make them into a people who might acknowledge him and serve him in holiness.” Jesus himself said, “I have come to serve not to be served,” (Mt 20:28), and he sends his Church out to serve and to imitate him when he says, “For as often as you eat this bread and drink the chalice, you proclaim the Lord’s death until he comes” (1 Cor 11:23-26).  
• CCC 1127: “Celebrated worthily in faith, the sacraments confer the grace that they signify. They are efficacious because in them Christ himself is at work: it is he who baptizes, he who acts in his sacraments in order to communicate the grace that each sacrament signifies. The Father always hears the prayer of his Son's Church which, in the epiclesis of each sacrament, expresses her faith in the power of the Spirit. As fire transforms into itself everything it touches, so the Holy Spirit transforms into the divine life whatever is subjected to his power.”
• CCC 1134: “The fruit of the sacramental life is both personal and ecclesial. For every one of the faithful on the one hand, this fruit is life for God in Jesus Christ; for the Church, on the other, it is an increase in charity and in her mission of the witness.”
• CCC 782: “One becomes a member of this people not by a physical birth; but by being “born anew”, a birth, “of water and Spirit”, that is, by faith in Christ, and Baptism.”