1. Notion and object of faith
The act of faith is man’s response to God who reveals himself (see Catechism , 142). “By faith, man completely submits his intellect and his will to God. With his whole being man gives his assent to God the revealer” ( Catechism, 143). Sacred Scripture calls this assent “obedience of faith” (See Rom 1:5, 16:26). The virtue of faith is a supernatural virtue which enables man, by enlightening his intellect and moving his will, to assent firmly to all that God has revealed, not because of the intrinsic evidence but because of the authority of God who is revealing. “Faith is first of all a personal adherence of man to God. At the same time, and inseparably, it is a free assent to the whole truth that God has revealed” ( Catechism, 150).
2. Characteristics of faith
— “ Faith is a gift of God, a supernatural virtue infused by him (see Mt 16:17). Before this faith can be exercised, man must have the grace of God” ( Catechism, 153).Reason does not suffice to enable one to embrace the revealed truth; the gift of faith is necessary.
— Faith is a human act. Although it is an act accomplished thanks to a supernatural gift, “believing is an authentically human act. Trusting in God and cleaving to the truths he has revealed is contrary neither to human freedom nor to human reason”( Catechism, 154).In faith, the intellect and will cooperate with God’s grace: “Faith is an act of the understanding which assents to the divine truth at the command of the will moved by God through grace.”  — Faith and freedom.“Man’s response to God by faith must be free, and . . . therefore nobody is to be forced to embrace the faith against his will. The act of faith is of its very nature a free act” ( Catechism, 160).  Christ invited people to faith and conversion, but never coerced them. “For he bore witness to the truth but refused to use force to impose it on those who spoke against it” ( Ibid .).
— Faith and reason. “Although faith is above reason, yet there can never be any real disagreement between faith and reason, since it is the same God who reveals mysteries and infuses faith and who has put the light of reason into the human soul. Now God cannot deny himself any more than the truth can ever contradict the truth.”  “Consequently, methodical research in all branches of knowledge, provided it is carried out in a truly scientific manner and does not override moral laws, can never conflict with the faith, because the things of the world and the things of faith derive from the same God” ( Catechism, 159).
It would be senseless to try to prove the supernatural truths of the faith; on the other hand, one can always prove that anything which claims to be contrary to these truths is false.
— The “ecclesiality” of faith. “To believe” is an act of a believer as a believer, that is to say, as a member of the Church. One who believes, assents to the truth taught by the Church, which guards the deposit of Revelation. “The Church’s faith precedes, engenders, supports and nourishes our faith. The Church is the mother of all believers” ( Catechism, 181) . “No one can have God as his Father who does not have the Church as his mother.” 
— Faith is necessary for salvation (see Mk 16:16; Catechism, 161). “Without faith it is impossible to please [God]” ( Heb 11:6). “Those who, through no fault of their own, do not know the Gospel of Christ or his Church, but who nevertheless seek God with a sincere heart, and, moved by grace, try in their actions to do his will as they know it through the dictates of their conscience—those too may achieve eternal salvation." 
3. The motives of credibility
“What moves us to believe is not the fact that revealed truths appear as true and intelligible in the light of our natural reason: we believe ‘because of the authority of God himself who reveals them, who can neither deceive nor be deceived’ ” ( Catechism, 156).
Nevertheless, in order for the act of faith to be in conformity with reason, God has wanted to give us “motives of credibility, which show that the assent of faith is by no means a blind impulse of the mind.”  The motives of credibility are sure signs that Revelation is the word of God.
These motives of credibility are, among others:
– the glorious Resurrection of our Lord Jesus Christ, a definitive sign of his divinity, and most certain proof of the truth of his words;
– “the miracles of Christ and the saints (see Mk 16:20; Acts 2:4)” ( Catechism, 156); 
– the fulfillment of the prophecies (see Catechism, 156) made about Christ or by Christ himself (for example, the prophecies about the passion of our Lord; the prophecy about the destruction of Jerusalem, etc.). This fulfillment is proof of the truthfulness of Sacred Scripture;
– the sublimity of Christian doctrine is also proof of its divine origin. Anyone who considers attentively the teachings of Christ, can discover in their profound truth, beauty and coherence, a wisdom which exceeds man’s capacity to understand and explain God’s nature, the world, and man’s transcendent meaning.
– the sanctity and spread of the Church, her fruitfulness and stability “are the most certain signs of divine Revelation, adapted to the intelligence of all” ( Catechism, 156).
The motives of credibility not only help those without faith to overcome their prejudices and accept it. They also strengthen those who already have faith, by confirming that it is reasonable to believe and preventing any “fideism.”
4. The knowledge of faith
Faith is a body of knowledge: by it we know natural and supernatural truths. The apparent obscurity which the believer experiences comes from the limitations of human intelligence when faced with the overwhelming light of divine truth. Faith is an anticipation of the vision of God “face to face: in heaven ( I Cor 13:12; see I Jn 3:2).
The certainty of faith: “ Faith is certain. It is more certain than all human knowledge because it is founded on the very word of God who cannot lie” ( Catechism, 157).“The certitude resulting from a divine light is greater than that which results from the light of natural reason.” 
Our intellect helps us to go deeper into the faith: “It is intrinsic to faith that a believer desires to know better the One in whom he has put his faith, and to understand better what He has revealed; a more penetrating knowledge will in turn call forth a greater faith, increasingly set afire by love” ( Catechism, 158).
Theology is the science of faith: it tries, with the help of reason, to grasp better the truths that we possess by faith; not in order to make them clearer in themselves – which is impossible – but to make them more intelligible to the believer. This effort, when authentic, stems from love for God and is accompanied by an effort to get closer to him. The greatest theologians have been and always will be the saints.
5. Consistency between faith and life
A Christian’s entire life should be a manifestation of faith. Every corner of one’s life should be illuminated by faith. “The just man lives by faith” ( Heb 2:4). Faith works through charity (see Gal 5:6) Without works, faith is dead (see Jas 2:20-26).
When this unity of life is missing, and one makes concessions to conduct not compatible with the faith, then one’s faith necessarily is weakened and is in danger of being lost.
Perseverance in the faith: Faith is a gratuitous gift of God. But we can lose this inestimable gift (see I Tim 1: 18–19). “To live, grow and persevere in the faith until the end we must nourish it” ( Catechism, 162). We should ask God to increase our faith (see Lk 17:5) and to make us “ fortes in fide ” ( I Pet 5:9). With God’s help, we should make many acts of faith.
All Catholic faithful are obliged to avoid dangers to their faith. Among other means, they should abstain from reading publications contrary to faith or morals—not only those that the magisterium of the Church has expressly pointed out, but also those recognized by a well-formed conscience—unless there is a grave reason and circumstances which make this reading safe.
Spreading the faith. “Nor do men light a lamp and put it under a bushel, but on a stand, and it gives light to all in the house. Let your light so shine before men” ( Mt 5:15-16). We have received the gift of faith in order to spread it, not to hide it (see Catechism, 166). We cannot set aside our faith in our professional activity.  We must shape the whole of society with Christ’s teachings and spirit.
The Catechism of the Catholic Church, 142-197.
The homily “Life of Faith,” in St. Josemaria, Friends of God , nos. 190-204.
 St. Thomas Aquinas, Summa Theologiae, II-II, q.2, a.9.
 Cf. Second Vatican Council, Declar. Dignitatis Humanae, 10: C.I.C., can. 748, ¤ 2.
 First Vatican Council; DS 3017.
 St. Cyprian, De Catholicae Unitate Ecclesiae: PL 4,503.
 Second Vatican Council, Const. Lumen Gentium, 16. .
 First Vatican Council: DS 3008–3010; Catechism of the Catholic Church, 156.
 The value of Sacred Scripture as a totally reliable historical source can be established by solid proofs; for example, showing its antiquity (some of the books of the New Testament were written only a few years after the death of Christ), or by the analysis of its contents (which shows the veracity of the testimonies).
 St. Thomas Aquinas, Summa Theologiae, II-II, q. 171, a.5, ad 3.
 See Saint Josemaria, The Way, 353.