Believe, then, your own books, and as to our Scriptures so much the more believe writings which are divine, but in the witness of the soul itself give like confidence to Nature. Choose the one of these you observe to be the most faithful friend of truth. If your own writings are distrusted, neither God nor Nature lie. And if you would have faith in God and Nature, have faith in the soul; thus you will believe yourself. Certainly you value the soul as giving you your true greatness—that to which you belong; which is all things to you; without which you can neither live nor die; on whose account you even put God away from you.
Since, then, you fear to become a Christian, call the soul before you, and put her to the question. Why does she worship another? Why name the name of God? Why does she speak of demons, when she means to denote spirits to be held accursed? Why does she make her protestations towards the heavens, and pronounce her ordinary execrations earthwards? Why does she render service in one place, in another invoke the Avenger? Why does she pass judgments on the dead? What Christian phrases are those she has got, though Christians she neither desires to see nor hear?
Why has she either bestowed them on us, or received them from us? Why has she either taught us them, or learned them as our scholar? Regard with suspicion this accordance in words, while there is such difference in practice. It is utter folly— denying a universal nature— to ascribe this exclusively to our language and the Greek, which are regarded among us as so near akin. The soul is not a boon from heaven to Latins and Greeks alone. Man is the one name belonging to every nation upon earth: there is one soul and many tongues, one spirit and various sounds; every country has its own speech, but the subjects of speech are common to all.
God is everywhere, and the goodness of God is everywhere; demons are everywhere, and the cursing of them is everywhere; the invocation of divine judgment is everywhere, death is everywhere, and the sense of death is everywhere, and all the world over is found the witness of the soul. There is not a soul of man that does not, from the light that is in itself, proclaim the very things we are not permitted to speak above our breath. Most justly, then, every soul is a culprit as well as a witness: in the measure that it testifies for truth, the guilt of error lies on it; and on the day of judgment it will stand before the courts of God, without a word to say.
You proclaimed God, O soul, but you did not seek to know Him: evil spirits were detested by you, and yet they were the objects of your adoration; the punishments of hell were foreseen by you, but no care was taken to avoid them; you had a savour of Christianity, and withal were the persecutor of Christians.
Source: The Soul's Testimony (New Advent)