Catholics believe in the Indwelling of the Holy Trinity-a grace given at baptism and throughout life in the Sacraments of the Church. God can give His sanctifying grace to whom He chooses, but we know that the Sacraments impart grace to the soul.
Here is a long section on holiness from the CCC.
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.
- After earth's exile, I hope to go and enjoy you in the fatherland, but I do not want to lay up merits for heaven. I want to work for your love alone. . . . In the evening of this life, I shall appear before you with empty hands, for I do not ask you, Lord, to count my works. All our justice is blemished in your eyes. I wish, then, to be clothed in your own justice and to receive from your love the eternal possession of yourself.63
2012 "We know that in everything God works for good with those who love him . . . For those whom he fore knew he also predestined to be conformed to the image of his Son, in order that he might be the first-born among many brethren. And those whom he predestined he also called; and those whom he called he also justified; and those whom he justified he also glorified."64
2013 "All Christians in any state or walk of life are called to the fullness of Christian life and to the perfection of charity."65 All are called to holiness: "Be perfect, as your heavenly Father is perfect."66
- In order to reach this perfection the faithful should use the strength dealt out to them by Christ's gift, so that . . . doing the will of the Father in everything, they may wholeheartedly devote themselves to the glory of God and to the service of their neighbor. Thus the holiness of the People of God will grow in fruitful abundance, as is clearly shown in the history of the Church through the lives of so many saints.67
2014 Spiritual progress tends toward ever more intimate union with Christ. This union is called "mystical" because it participates in the mystery of Christ through the sacraments - "the holy mysteries" - and, in him, in the mystery of the Holy Trinity. God calls us all to this intimate union with him, even if the special graces or extraordinary signs of this mystical life are granted only to some for the sake of manifesting the gratuitous gift given to all.
2015 The way of perfection passes by way of the Cross. There is no holiness without renunciation and spiritual battle.68 Spiritual progress entails the ascesis and mortification that gradually lead to living in the peace and joy of the Beatitudes:
- He who climbs never stops going from beginning to beginning, through beginnings that have no end. He never stops desiring what he already knows.69
2016 The children of our holy mother the Church rightly hope for the grace of final perseverance and the recompense of God their Father for the good works accomplished with his grace in communion with Jesus.70Keeping the same rule of life, believers share the "blessed hope" of those whom the divine mercy gathers into the "holy city, the new Jerusalem, coming down out of heaven from God, prepared as a bride adorned for her husband."71
2017 The grace of the Holy Spirit confers upon us the righteousness of God. Uniting us by faith and Baptism to the Passion and Resurrection of Christ, the Spirit makes us sharers in his life.
2018 Like conversion, justification has two aspects. Moved by grace, man turns toward God and away from sin, and so accepts forgiveness and righteousness from on high.
2019 Justification includes the remission of sins, sanctification, and the renewal of the inner man.
2020 Justification has been merited for us by the Passion of Christ. It is granted us through Baptism. It conforms us to the righteousness of God, who justifies us. It has for its goal the glory of God and of Christ, and the gift of eternal life. It is the most excellent work of God's mercy.
2021 Grace is the help God gives us to respond to our vocation of becoming his adopted sons. It introduces us into the intimacy of the Trinitarian life.
2022 The divine initiative in the work of grace precedes, prepares, and elicits the free response of man. Grace responds to the deepest yearnings of human freedom, calls freedom to cooperate with it, and perfects freedom.
2023 Sanctifying grace is the gratuitous gift of his life that God makes to us; it is infused by the Holy Spirit into the soul to heal it of sin and to sanctify it.
2024 Sanctifying grace makes us "pleasing to God." Charisms, special graces of the Holy Spirit, are oriented to sanctifying grace and are intended for the common good of the Church. God also acts through many actual graces, to be distinguished from habitual grace which is permanent in us.
2025 We can have merit in God's sight only because of God's free plan to associate man with the work of his grace. Merit is to be ascribed in the first place to the grace of God, and secondly to man's collaboration. Man's merit is due to God.
2026 The grace of the Holy Spirit can confer true merit on us, by virtue of our adoptive filiation, and in accordance with God's gratuitous justice. Charity is the principal source of merit in us before God.
2027 No one can merit the initial grace which is at the origin of conversion. Moved by the Holy Spirit, we can merit for ourselves and for others all the graces needed to attain eternal life, as well as necessary temporal goods.
2028 "All Christians . . . are called to the fullness of Christian life and to the perfection of charity" (LG 40 § 2). "Christian perfection has but one limit, that of having none" (St. Gregory of Nyssa, De vita Mos.:PG 44, 300D).
2029 "If any man would come after me, let him deny himself and take up his cross and follow me" (Mt 16:24).
And how do we know we can get sanctifying grace: here is the CCC again.
1212 The sacraments of Christian initiation - Baptism, Confirmation, and the Eucharist - lay the foundations of every Christian life. "The sharing in the divine nature given to men through the grace of Christ bears a certain likeness to the origin, development, and nourishing of natural life. The faithful are born anew by Baptism, strengthened by the sacrament of Confirmation, and receive in the Eucharist the food of eternal life. By means of these sacraments of Christian initiation, they thus receive in increasing measure the treasures of the divine life and advance toward the perfection of charity."
To be continued....two more tomorrow.