We all want good things, when we encounter something good, whether it be the type of food, or car, or smartphone, our first question is often: where can I get that?

Virtue is a good thing. A virtuous person possesses an undeniable appeal. A virtuous person can inspire us to pursue virtue ourselves, but this is where things become somewhat complex. Unlike food, a car, or a smartphone, the virtues are not external, material things that I can obtain and then place in my refrigerator, my garage, or my pocket. Virtues are things inhere inside of a person. Human persons do not have virtues so much as they are virtuous. And this is good news, although multiple cannot all have an individual smartphone at the same time and to the same degree, everyone has the potential to be truly virtuous and enjoy the happy freedom that virtue provides. But where do we get virtue? Where does virtue come from? What makes a person virtuous? Let us look at the causes of the virtues.

We recall that the virtues perfect the human person, and in that person’s actions good. A virtue is a kind of habit that is a stable disposition that profoundly qualifies (deeply ) that human powers of knowing, willing, and feeling.

A virtuous person performs good actions because he or she is a good person. The type of actions one performs is linked to the type of person one is. We also recall that there are two broad categories of virtue: there are, first of all, moral virtues or human virtues. These virtues perfect the human power of knowing, being willing, and feeling in a human way and on a human level. The most famous example of the virtuous is the habits of prudence, justice fortitude, and temperance.

These pivotal ( or cardinal ) virtues perfect the natural powers of knowing, being willing, and feeling in a way proportioned to natural human freedom and flourishing.

The second broad category of virtue is the theological or God’s virtues. These virtues perfect and extend the human powers of knowing and willing beyond the human person to God himself. These operate on a supernatural level. There are three theological virtues: faith, hope, and charity. Let us now turn to the causes of these two types of virtues. A natural cause of moral ( or human ) virtues is the performance of good actions. For example, take a man who interacts with others. Such a man encounters residential neighbors and works colleagues on a regular basis. As a human being, this man of course has a will;  and thus, he has the potential to exercise his will justly in his dealings with others.  If he acts justly if he gives to others that which they are owed, that which is their due, he eventually becomes a just man. The man who acts justly with regularity eventually acquires the habit of justice in his will. Why? Because through the deliberate and repeated acts of justice he becomes accustomed. He becomes habituated to the form of justice. His will itself takes on the just shape of his just actions. He becomes what he does. And because his actions are just, he becomes a just person. Similarly, the man who acts temperately, the man who allows reason to guide his enjoyment of physical pleasure like food and drink eventually becomes a temperate man.

He is a man who desires to take on the virtuous shape, the liberating habit of temperance.  Through deliberate and repeated eating healthy proportions ( pursuing the good and virtuous means between excess ( too much ) and defect (too little) the man becomes a temperate man.

In summary, the natural cause of moral virtue is the performance of good actions. Moral virtues can be acquired through virtuous activity. The more good that we do, the more virtuous we become. And the more virtuous we become, the more promptly, joyfully, and easily do we perform good actions, We become what we do. 

There is another type of virtue that no human action can still in the soul of the person. And these are the infuse virtues, the virtues that direct and unite us to God. God is the principal cause of the infused virtues. In the case of acquired virtues, repeated, good actions eventually yield a virtuous habit in the powers of the human soul. In this case of infused virtues, however, this order is reversed. God first imparts, He first infuses, supernatural virtue into the soul, and then the person is able to act according to these theological virtues.

Why do we need infused supernatural virtues? As discussed earlier, the acquired moral virtues are habits that are good in relation to human goodness. The moral virtues are good insofar as they perfect nature on a natural level. In contrast, the infused virtues are supernatural good. They are with goodness beyond the proportion of human goodness. God is the measure of supernatural goodness. And because the intimate life of God is beyond the natural reach of the human powers of knowing and willing, only God can cause the theological virtues in the power of the human soul. Take the infused (theological) virtue as faith, for example; no repeated acts of rigorous thought or even sympathetic judgment can engender or cause the supernatural virtue of faith in the human intellect. We do not come to faith in God after or because we have to judge what he says to be true. Rather, God first imparts the theological virtue of faith in the soul, and it is by this supernatural habit that we are enabled to make acts of faith.

The theological virtue of faith unites the human intellect to God. Through faith, we believe that what God reveals is true because it is God who reveals it. Our mind must first be raised to God in order for us to believe something because of God. This is what the infused virtue does.

In sum, the virtues perfect a human person, making both the person and the person actions good. But there are two kinds of goodness: There is natural (moral) goodness and there is supernatural (theological) goodness. We acquired moral virtues through repeated actions. In this way, good actions are the cause of moral virtue in the human powers of knowing, willing, and feeling.

With regard to supernatural goodness, the goodness of God, however, no human action can produce theologically proportioned virtues. Only God can cause, only God infuses his virtues: faith, hope, and charity. Therefore, repeated and deliberate good actions can cause moral virtue. But only God can cause the infused virtues in the soul of the human person.

Summa Theologiae I-II, q. 51, a,1-3)
https://aquinas101.thomisticinstitute.org