Faith in the Catechism of the Summa Theologica

Is the recitation of the Apostles' Creed an act of faith "par excellence"?
Yes, indeed it cannot be sufficiently recommended to the faithful for their daily practice.

Is it possible to make a short and concise act of faith?
Yes; the following in the form of an act of homage to God is excellent: "O my God, I believe, on Thy word, all that Thou hast revealed to us, because of Thyself who hast promised to be some day our perfect happiness."

Who are able to make this act of faith ?
Those only who have the supernatural virtue of faith (IV., V.).

Then unbelievers cannot make this act of faith?
No, for they do not believe what God has revealed with a view to their supernatural happiness; and this either because they are ignorant thereof, or do not trust in the will of God, who is able to give to them the good that He thinks fit; or because having known His revelation they refuse to give their assent to it (X.).

Can the impious make this act of faith ?
No, because even though they may hold to be true what God has revealed by reason of the authority of God, who can neither deceive nor be deceived, their assent is not the effect of a supernatural love for the word of God; on the contrary, the word of God is hateful to them, although in spite of themselves they are forced to admit its truth (V. 2, ad 2).

Are there men who believe the word of God, and yet do not make an act of the supernatural virtue?
Yes, and in this they imitate the devils (V. 2).

Can heretics make an act of faith ?
No, for even though in their minds they assent to such and such a point of revealed doctrine, they do not give this assent on the word of God, but on their own private judgment (V. 3).

As regards the act of faith, are heretics more to be blamed than the impious or the devils?
Yes, because the word of God or His authority is not the motive of their assent.

Can apostates make an act of faith ?
No, because their mind rejects entirely what formerly they believed on the word of God (XII.).

Can sinners make an act of faith ?
Yes, provided they actually have this virtue; and they can have it, although imperfectly, when they have not charity, that is when they are in the state of mortal sin (IV. i, 4).

Every mortal sin then is not a sin against faith?
No (X. 1,4).

In what consists precisely a sin against faith?
A sin against faith consists in not wishing to submit one's mind to the word of God through homage or through love for God s word (X. 1-3).

Is it always man's own fault if he does not thus submit his mind to the word of God through homage or through love for God's word?
Yes, it is always man's own fault, because he resists the actual grace God offers inviting him to make this act of submission (VI. 1,2).

Is this actual grace offered to all men on earth?
Yes, all men always have this grace, although in different degrees and as it pleases God to distribute it according to the designs of His Providence.

Is it a great grace of God to have the virtue of supernatural faith?
Yes, to have the supernatural virtue of faith is in some sense the greatest grace of God.

Why is the gift of faith the greatest grace of God?
Because, without supernatural faith one can do absolutely nothing towards salvation; moreover, heaven is lost unless one receive the gift of faith from God before death (II. 5-8; IV. 7).

Would it then be a great sin to expose oneself to the danger of losing the happiness of its possession by reading books or by listening to conversations opposed thereto?
Yes, it would be a great sin to place oneself knowingly in this danger; and even when it is not one's own fault, it is a deplorable thing to have to run such danger.

It is then an extremely important thing to choose our acquaintances and our reading with prudence so as not to expose ourselves to this danger, but, on the contrary, so as to preserve and to increase the great gift of faith?
Yes, this is extremely important, especially seeing that in the world, what with the liberty of the press and so forth, one meets so many things that are dangerous to faith.

Is there any other sin against faith?
Yes, the sin of blasphemy (XIII.).

Why is blasphemy a sin against faith?
Because it militates directly against the exterior act of faith which is the confession of faith by words; all blasphemy, in fact, consists in the uttering of some word that dishonours God or His saints (XIII. i).

Is blasphemy a great sin?
Blasphemy is always of its nature a great sin (XIII. 2-3).

Does the habit of blaspheming excuse or lessen the gravity of the sin?
On the contrary, this habit aggravates the sin somewhat, for instead of endeavouring to correct oneself of the habit, the grave evil is allowed to become rooted firmly (XIII. 2, ad 3).

Fr. R.P. Pegues, O.P. - Catechism of the Summa Theologica of St. Thomas Aquinas

Act of Faith

O My God! I firmly believe in one God in three Divine Persons -- the Father, the Son and the Holy Ghost; I believe in Jesus Christ, the true and only Son of God, Who was born of the Virgin Mary, and died on the Cross for our salvation; I also believe all the sacred truths the Catholic Church believes and teaches, because Thou hast revealed them, Who canst neither deceive nor be deceived.

'It is a certain, well established fact that no other crime so seriously offends God and provokes His greatest wrath as the vice of heresy. Nothing contributes more to the down fall of provinces and kingdoms than this frightful pest.'

St. Charles Borromeo

'Blessed the one who has shone by the light of faith of the Lord, like a radiant lamp on a tall lampstand, and has enlightened souls that are darkened, for they followed the heresy of the faithless and impious.'

St. Ephrem of Syria