The Athanasian Creed was not written by St. Athanasius, the defender of the doctrine of the Trinity at the Council of Nicaea (AD 325). It seems to have been written about a hundred years later. This creed expands the teaching of the Trinity, and seems to draw from a work by St. Augustine, On the Trinity, from AD 415. The oldest surviving manuscripts of the Athanasian Creed date from the late 8th century. One scholar commented that it reads like the minutes of the Council of Nicaea, with the arguments for the Trinity being presented, and the arguments against it (some repetitive and petulant) being refuted.
The use of the word catholic (note the small c) is referring to the universal Christian faith taught in the scriptures and believed by the Christian faithful.
Traditionally the Athanasian Creed was used in the early morning office of Prime in place of the psalm during the Sundays after Epiphany and Sundays after Pentecost, including Trinity Sunday. Today the Athanasian Creed is sometimes used on Trinity Sunday.
1 Whoever wants to be saved should above all cling to the catholic faith.
2 Whoever does not guard it whole and inviolable will doubtless perish eternally.
3 Now this is the catholic faith:
4 We worship one God in trinity and the Trinity in unity, neither confusing the persons nor dividing the divine being.
5 For the Father is one person, the Son is another, and the Spirit is still another.
6 But the deity of the Father, Son, and Holy Spirit is one, equal in glory, coeternal in majesty.
7 What the Father is, the Son is, and so is the Holy Spirit.
8 Uncreated is the Father; uncreated is the Son; uncreated is the Spirit.
9 The Father is infinite; the Son is infinite; the Holy Spirit is infinite.
10 Eternal is the Father; eternal is the Son; eternal is the Spirit.
11 And yet there are not three eternal beings, but one who is eternal;
12 as there are not three uncreated and unlimited beings, but one who is uncreated and unlimited.
13 Almighty is the Father; almighty is the Son; almighty is the Spirit:
14 And yet there are not three almighty beings, but one who is almighty.
15 Thus the Father is God; the Son is God; the Holy Spirit is God:
16 And yet there are not three gods, but one God.
17 Thus the Father is Lord; the Son is Lord; the Holy Spirit is Lord:
18 And yet there are not three lords, but one Lord.
19 As Christian truth compels us to acknowledge each distinct person as God and Lord, so catholic religion forbids us to say that there are three gods or lords.
20 The Father was neither made nor created nor begotten;
21 the Son was neither made nor created, but was alone begotten of the Father;
22 the Spirit was neither made nor created, but is proceeding from the Father and the Son.
23 Thus there is one Father, not three fathers; one Son, not three sons; one Holy Spirit, not three spirits.
24 And in this Trinity, no one is before or after, greater or less than the other;
25 but all three persons are in themselves, coeternal and coequal; and so we must worship the Trinity in unity and the one God in three persons.
26 Whoever wants to be saved should think thus about the Trinity.
27 It is necessary for eternal salvation that one also faithfully believe that our Lord Jesus Christ became flesh.
28 For this is the true faith that we believe and confess: That our Lord Jesus Christ, God’s Son, is both God and man.
29 He is God, begotten before all worlds from the being of the Father, and he is man, born in the world from the being of his mother —
30 existing fully as God, and fully as man with a rational soul and a human body;
31 equal to the Father in divinity, subordinate to the Father in humanity.
32 Although he is God and man, he is not divided, but is one Christ.
33 He is united because God has taken humanity into himself; he does not transform deity into humanity
34 He is completely one in the unity of his person, without confusing his natures.
35 For as the rational soul and body are one person, so the one Christ is God and man.
36 He suffered death for our salvation.
He descended into hell and rose again from the dead.
37 He ascended into heaven and is seated at the right hand of the Father.
He will come again to judge the living and the dead.
38 At his coming all people shall rise bodily to give an account of their own deeds.
39 Those who have done good will enter eternal life,
those who have done evil will enter eternal fire.
40 This is the catholic faith.
One cannot be saved without believing this firmly and faithfully.
Source: This translation is from Christianity Knowledge Base at Fandom.com, and appears to be based on the English translation in the Book of Common Prayer.
Original in Latin:
Quicumque vult salvus esse, ante omnia opus est, ut teneat catholicam fidem:
Quam nisi quisque integram inviolatamque servaverit, absque dubio in aeternum peribit.
Fides autem catholica haec est:
ut unum Deum in Trinitate, et Trinitatem in unitate veneremur.
Neque confundentes personas, neque substantiam separantes.
Alia est enim persona Patris alia Filii, alia Spiritus Sancti:
Sed Patris, et Filii, et Spiritus Sancti una est divinitas, aequalis gloria, coeterna maiestas.
Qualis Pater, talis Filius, talis [et] Spiritus Sanctus.
Increatus Pater, increatus Filius, increatus [et] Spiritus Sanctus.
Immensus Pater, immensus Filius, immensus [et] Spiritus Sanctus.
Aeternus Pater, aeternus Filius, aeternus [et] Spiritus Sanctus.
Et tamen non tres aeterni, sed unus aeternus.
Sicut non tres increati, nec tres immensi, sed unus increatus, et unus immensus.
Similiter omnipotens Pater, omnipotens Filius, omnipotens [et] Spiritus Sanctus.
Et tamen non tres omnipotentes, sed unus omnipotens.
Ita Deus Pater, Deus Filius, Deus [et] Spiritus Sanctus.
Et tamen non tres dii, sed unus est Deus.
Ita Dominus Pater, Dominus Filius, Dominus [et] Spiritus Sanctus.
Et tamen non tres Domini, sed unus [est] Dominus.
Quia, sicut singillatim unamquamque personam Deum ac Dominum confiteri christiana veritate compellimur:
Ita tres Deos aut [tres] Dominos dicere catholica religione prohibemur.
Pater a nullo est factus: nec creatus, nec genitus.
Filius a Patre solo est: non factus, nec creatus, sed genitus.
Spiritus Sanctus a Patre et Filio: non factus, nec creatus, nec genitus, sed procedens.
Unus ergo Pater, non tres Patres: unus Filius, non tres Filii: unus Spiritus Sanctus, non tres Spiritus Sancti.
Et in hac Trinitate nihil prius aut posterius, nihil maius aut minus:
Sed totae tres personae coaeternae sibi sunt et coaequales.
Ita, ut per omnia, sicut iam supra dictum est, et unitas in Trinitate, et Trinitas in unitate veneranda sit.
Qui vult ergo salvus esse, ita de Trinitate sentiat.
Sed necessarium est ad aeternam salutem, ut incarnationem quoque Domini nostri Iesu Christi fideliter credat.
Est ergo fides recta ut credamus et confiteamur, quia Dominus noster Iesus Christus, Dei Filius, Deus [pariter] et homo est.
Deus [est] ex substantia Patris ante saecula genitus: et homo est ex substantia matris in saeculo natus.
Perfectus Deus, perfectus homo:
ex anima rationali et humana carne subsistens.
Aequalis Patri secundum divinitatem: minor Patre secundum humanitatem.
Qui licet Deus sit et homo, non duo tamen, sed unus est Christus.
Unus autem non conversione divinitatis in carnem, sed assumptione humanitatis in Deum.
Unus omnino, non confusione substantiae, sed unitate personae.
Nam sicut anima rationalis et caro unus est homo: ita Deus et homo unus est Christus.
Qui passus est pro salute nostra:
descendit ad inferos:
tertia die resurrexit a mortuis.
Ascendit ad [in] caelos, sedet ad dexteram [Dei] Patris [omnipotentis].
Inde venturus [est] judicare vivos et mortuos.
Ad cujus adventum omnes homines resurgere habent cum corporibus suis;
Et reddituri sunt de factis propriis rationem.
Et qui bona egerunt, ibunt in vitam aeternam:
qui vero mala, in ignem aeternum.
Haec est fides catholica, quam nisi quisque fideliter firmiterque crediderit, salvus esse non poterit.