Second, faith is understood to be a virtue. Virtues are habits that incline us to perform good acts. The virtue of faith is the habit, that is, the ability and disposition that help us to make the act of faith. 

Third, faith refers to the body of truths, the deposit of faith. This is what we mean when we say the Catholic Faith. Let us look at these more closely.

When we talk about faith as a body of truths, we are referring to content. We are saying that we believe certain truths on the authority of God having revealed them. At different times in history, the Church has listed the main revealed truths in formulas called creeds. These creeds contain the teachings of the Church. The Nicene-Constantinopolitan creed that is regularly recited at Mass after the homily holds a very special place as an expression of Church teaching—since it reflects the ancient faith of the Church in God’s Trinitarian nature. There is a portion of this creed devoted to each Person of the Holy Trinity. In the Catholic faith this is fundamental, since everything the Church believes derives ultimately from God’s Trinitarian nature. This is why the Catechism of the Catholic Church is largely an expansion of this creed.

As we have said, this body of truths, the faith, requires an act of assent or agreement on our part. This acceptance is the act of faith. This response to God's revelation is an act of obedience to what God has asked us to believe. By ourselves we cannot perform such acts, so we need help. Such help is called grace and comes to us all through life in the form of impulses of the Holy Spirit.

These are called actual graces. The disposition to make such an act of faith comes to us as a gift at Baptism. However, this is only in a relatively permanent way. The reason is that as a virtue faith is a gift that of itself is lasting. But it can be lost by a free denial of one's faith.

There are three theological virtues: faith, hope and charity. They are called theological because they pertain directly to God. They are called virtues because they are habits that help us to act. Therefore, they have God Himself as the direct object when the particular virtue is translated into an act. 

Since our concern here is with the virtue of faith, let us look at it first.
Faith, as a virtue, is the habit that enables us with God's grace to perform the good action of believing. It is the power to know God as He has revealed Himself. Once we have known Him, the virtue of faith enables us to keep strong in that belief even when the world threatens to destroy our faith.

Hope, as a virtue, gives us the ability to trust God and disposes us to want to be with Him forever.

Charity, as a virtue, gives us the power to love God, and, once loving Him, it enables us to love our neighbor as Christ, who is God, loves us: "A new commandment I give to you, that you love one another; even as I have loved you, that you also love one another" (John 13:34).

There is a direct relationship between faith and revelation. Revelation, as we have said, is God speaking to man, and faith is man listening and responding to God.
We could say, if we carefully understand what we mean, that revelation is similar to a cause relative to its effect. What is a cause? A cause is something from which another thing proceeds and upon which it depends for its existence. By its very presence and acting, it produces the effect, assuming that all things required for the effect are present. Now, while revelation is similar to this, there is nevertheless a difference. Revelation by its mere presence does not actually make man believe, and revelation does not automatically produce faith. God by the free giving of revelation, causes the reasonableness of believing to be discoverable through the grace that He gives. This grace illumines the mind and inclines the will. Cooperating with this grace, man is able freely to choose to consider the fact of revelation and freely to assent to it. But God does not make man freely consider or freely accept.

What then is the act of faith? The act of faith can be broken down into several steps. First, the person recognizes a truth that is revealed. Second, the person perceives the reasonableness of assenting to this particular revealed truth. Third, the person actually gives the assent to the truth. Fourth, the person thereby gives assent to God who is revealing the truth.

Although it is the mind that makes this assent to the revealed truth, we cannot reduce this simply to an act of the intellect. Since it is a human act, it involves both the intellect and the will. The mind sees that it is morally good to assent to what the Church presents as being the Word of God. Nevertheless, the mind assents only because the will, previously attracted and solicited by grace, freely consents.

The more often that we make acts of belief, explicitly or implicitly, the more we will want to listen to God revealed in Jesus. What is important to remember about revelation is that God wants us to know about Him. This is why He reveals himself naturally and supernaturally. If we freely accept his first gift of grace, he will continue to give other graces and continue to lead us to a deeper and deeper faith. We cannot of ourselves cause our faith, but we can freely respond to the inspiration to listen and eventually freely to accept. The Lord freely gives to us what we cannot give ourselves, a belief in him that supports our ability to trust him. Trusting him we have the courage to let God come closer to us. As a result we develop courage to trust others and to love others and to open ourselves to their love for us.