The Catechism on Salvation by GraceThis fact that Catholics believe in salvation by grace through faith is the first and most important thing to establish before any discussion on salvation can be undertaken. If you, as a Catholic, begin by discussing the importance of the sacraments, or of good works, or merit, or indulgences, or anything else, then you will simply be talking past your opponent. After all, he probably enters the discussion already thinking that Catholics are Pelagian and so will filter any talk of sacraments, or works, or merit through that misunderstanding. But, once you lay the groundwork by affirming what he himself believes, then you can begin to show how sacraments and everything else fits within that belief in the primacy of grace and faith.
684 Through his grace, the Holy Spirit is the first to awaken faith in us and to communicate to us the new life, which is to "know the Father and the one whom he has sent, Jesus Christ."
1949 Called to beatitude but wounded by sin, man stands in need of salvation from God. Divine help comes to him in Christ through the law that guides him and the grace that sustains him:
“Work out your own salvation with fear and trembling; for God is at work in you, both to will and to work for his good pleasure.” (Phil 2:12-13)1989 The first work of the grace of the Holy Spirit is conversion, effecting justification in accordance with Jesus' proclamation at the beginning of the Gospel: "Repent, for the kingdom of heaven is at hand."
1996 Our justification comes from the grace of God. Grace is favor, the free and undeserved help that God gives us to respond to his call to become children of God, adoptive sons, partakers of the divine nature and of eternal life.
1998 This vocation to eternal life is supernatural. It depends entirely on God's gratuitous initiative, for he alone can reveal and give himself. It surpasses the power of human intellect and will, as that of every other creature.
1999 The grace of Christ is the gratuitous gift that God makes to us of his own life, infused by the Holy Spirit into our soul to heal it of sin and to sanctify it.
2003 Grace is first and foremost the gift of the Spirit who justifies and sanctifies us.
2010 Since the initiative belongs to God in the order of grace, no one can merit the initial grace of forgiveness and justification, at the beginning of conversion.
2011 The charity of Christ is the source in us of all our merits before God. Grace, by uniting us to Christ in active love, ensures the supernatural quality of our acts and consequently their merit before God and before men. The saints have always had a lively awareness that their merits were pure grace.
The Catechism on Salvation by Faith
161 Believing in Jesus Christ and in the One who sent him for our salvation is necessary for obtaining that salvation. "Since 'without faith it is impossible to please [God]' and to attain to the fellowship of his sons, therefore without faith no one has ever attained justification, nor will anyone obtain eternal life 'But he who endures to the end.'"
183 Faith is necessary for salvation. The Lord himself affirms: "He who believes and is baptized will be saved; but he who does not believe will be condemned" (Mk 16:16).
1816 Service of and witness to the faith are necessary for salvation: "So every one who acknowledges me before men, I also will acknowledge before my Father who is in heaven; but whoever denies me before men, I also will deny before my Father who is in heaven" (Mt 10:32-33).
The Catechism on Salvation by Grace and Faith
153 Faith is a grace. When St. Peter confessed that Jesus is the Christ, the Son of the living God, Jesus declared to him that this revelation did not come "from flesh and blood", but from "my Father who is in heaven". Faith is a gift of God, a supernatural virtue infused by him. "Before this faith can be exercised, man must have the grace of God to move and assist him; he must have the interior helps of the Holy Spirit, who moves the heart and converts it to God, who opens the eyes of the mind and 'makes it easy for all to accept and believe the truth.'"
1966 The New Law is the grace of the Holy Spirit given to the faithful through faith in Christ.
2001 The preparation of man for the reception of grace is already a work of grace. This latter is needed to arouse and sustain our collaboration in justification through faith, and in sanctification through charity. God brings to completion in us what he has begun, "since he who completes his work by cooperating with our will began by working so that we might will it:"“Indeed we also work, but we are only collaborating with God who works, for his mercy has gone before us. It has gone before us so that we may be healed, and follows us so that once healed, we may be given life; it goes before us so that we may be called, and follows us so that we may be glorified; it goes before us so that we may live devoutly, and follows us so that we may always live with God: for without him we can do nothing.”
Dave Armstrong has done excellent work towards achieving that end. See, for example:
- Dialogue on Catholic Soteriology (Specifically Grace)
- Biblical Evidence for the Nature of Saving Faith
- Catholic "Initial Justification" and Protestant "Faith Alone": Significant Common Ground?
- Monergism as a Characteristic of Initial Justification: Documented from Trent, Vatican I, and the Catechism of the Catholic Church
- Ecumenical Discussion on Comparative Protestant-Catholic Soteriology
- Catholic Underemphasis on Justification by Faith: My Theory on Why That Is
- Do Catholics Believe in Imputed Justification, External Righteousness, and Justification by Faith Alone? Yes (!), with Proper Biblical Qualifications