Quicumque

Though it is not an act specifically granted an indulgence under the Enchiridion, it would still be a good thing to recall and recite the Quicumque, or the Athanasian Creed today.

WHOEVER wishes to be saved must, above all, keep the Catholic faith.
For unless a person keeps this faith whole and entire, he will undoubtedly be lost forever.
This is what the catholic faith teaches: we worship one God in the Trinity and the Trinity in unity.
Neither confounding the Persons, nor dividing the substance.
For there is one person of the Father, another of the Son, another of the Holy Spirit.
But the Father and the Son and the Holy Spirit have one divinity, equal glory, and coeternal majesty.
What the Father is, the Son is, and the Holy Spirit is.
The Father is uncreated, the Son is uncreated, and the Holy Spirit is uncreated.
The Father is boundless, the Son is boundless, and the Holy Spirit is boundless.
The Father is eternal, the Son is eternal, and the Holy Spirit is eternal.
Nevertheless, there are not three eternal beings, but one eternal being.
So there are not three uncreated beings, nor three boundless beings, but one uncreated being and one boundless being.
Likewise, the Father is omnipotent, the Son is omnipotent, the Holy Spirit is omnipotent.
Yet there are not three omnipotent beings, but one omnipotent being.
Thus the Father is God, the Son is God, and the Holy Spirit is God.
However, there are not three gods, but one God.
The Father is Lord, the Son is Lord, and the Holy Spirit is Lord.
However, there are not three lords, but one Lord.
For as we are obliged by Christian truth to acknowledge every Person singly to be God and Lord, so too are we forbidden by the Catholic religion to say that there are three Gods or Lords.
The Father was not made, nor created, nor generated by anyone.
The Son is not made, nor created, but begotten by the Father alone.
The Holy Spirit is not made, nor created, nor generated, but proceeds from the Father and the Son.
There is, then, one Father, not three Fathers; one Son, not three sons; one Holy Spirit, not three holy spirits.
In this Trinity, there is nothing before or after, nothing greater or less. The entire three Persons are coeternal and coequal with one another.
So that in all things, as is has been said above, the Unity is to be worshiped in Trinity and the Trinity in Unity.
He, therefore, who wishes to be saved, must believe thus about the Trinity.
It is also necessary for eternal salvation that he believes steadfastly in the incarnation of our Lord Jesus Christ.
Thus the right faith is that we believe and confess that our Lord Jesus Christ, the Son of God, is both God and man.
As God, He was begotten of the substance of the Father before time; as man, He was born in time of the substance of His Mother.
He is perfect God; and He is perfect man, with a rational soul and human flesh.
He is equal to the Father in His divinity, but inferior to the Father in His humanity.
Although He is God and man, He is not two, but one Christ.
And He is one, not because His divinity was changed into flesh, but because His humanity was assumed unto God.
He is one, not by a mingling of substances, but by unity of person.
As a rational soul and flesh are one man: so God and man are one Christ.
He died for our salvation, descended into hell, and rose from the dead on the third day.
He ascended into heaven, sits at the right hand of God the Father almighty. From there He shall come to judge the living and the dead.
At His coming, all men are to arise with their own bodies; and they are to give an account of their own deeds.
Those who have done good deeds will go into eternal life; those who have done evil will go into the everlasting fire.
This is the Catholic faith. Everyone must believe it, firmly and steadfastly; otherwise He cannot be saved. Amen.

One of the symbols of the faith. Chock full of goodness, and especially nice for the feast of the Most Holy Trinity.