Romans 2:14-15
When Gentiles, who do not have the law, by nature do the things contained in the law, these, although not having the law, are a law to themselves, who show the work of the law written in their hearts, their conscience also bearing witness.
Justin Martyr
Those who did that which is universally, naturally, and eternally good are pleasing to God. Therefore, in the resurrection, they will be saved through this Christ. They will be saved equally with those righteous men who were before them—namely, Noah, Enoch, Jacob, and whoever else there may be—along with those who have known this Christ. (AD 160)
For God sets before every race of mankind that which is always and universally just, as well as all righteousness. Every race knows that adultery, fornication, homicide, and similar things are sinful. And though they all commit such practices, yet they do not escape from the knowledge that they act unrighteously whenever they do so. (AD 160)
Irenaeus
However, God exercises a providence over all things. Therefore, He also gives counsel. When giving counsel, He is present with those who attend to moral discipline. It follows, of course, that the subjects who are watched over and governed should be acquainted with their ruler. . . . For this reason, some of the Gentiles who were less addicted to allurements and immorality (and were not led away to such a degree of superstition concerning idols) were somewhat moved by His providence. Therefore, they were convinced that they should call the Maker of this universe the Father, for He exercises a providence over all things and arranges the affairs of our world. . . . Therefore, the God who benevolently causes His sun to rise upon everyone and sends rain upon both the just and the unjust, will judge those who, although enjoying His equally distributed kindness, have led lives not corresponding to the dignity of His generosity. (AD 160)
Clement of Alexandria
At the most, the Greeks have received certain scintillations of the divine Word. For that reason, they have made some utterances of truth. Therefore, they bear witness that the force of truth is not hidden. Yet, at the same time, they expose their own weakness in not having arrived at the end. (AD 195)
Tertullian
I contend that, before the Law of Moses was written on stone tablets, there was an unwritten, natural law that was habitually understood and that the fathers habitually kept. (AD 197)
Although good and evil are each known by nature, yet life is not thereby spent under the discipline of God. (AD 207)
Both the people [of Israel], by their transgression of His laws, and the whole race of mankind, by their neglect of natural duty, had sinned and rebelled against the Creator. (AD 207)
Origen
The Lord Himself says, “If I had not come and spoken unto them, they would have no sin. But now they have no cloak for their sin.” The only sense we can find in His words is that the Logos [Reason] Himself says that persons are not chargeable with sin to whom He has not fully come. However, those who have had part in Him—but act contrary to the ideas by which He declares His full presence in us—are guilty if they sin. Only when read in that manner is the saying true. . . . However, if the words are applied to the visible Christ (as many think that they should), then is it really true that those had no sin to whom He did not come? If so, then all who lived before the coming of the Savior were free from sin. For Jesus, as seen in the flesh, had not yet come. What is more, all those to whom He has never been preached will have no sin. And if they have no sin, then it is clear they are not liable to judgment. However, our whole race has part in the logos [reason] in man. . . . For before the consummation of logos [reason] comes, there is nothing in man except what is blameworthy. All is imperfect and defective. (AD 228)
It is no matter of surprise that the same God would have sown in the hearts of all men those truths that he taught by the prophets and the Savior. This was so that at the divine Judgment every man will be without excuse, having the “requirements of the law written upon his heart.” (AD 248)
Plato . . . in one of his epistles talks about the “chief good” and says, “The chief good can by no means be described in words. Rather, it is produced by long habit, and it bursts forth suddenly as a light in the soul.” . . . On hearing these words, we then admit that they are well said. For it is God who revealed to men these and other noble expressions. It is for this reason that those who have entertained correct ideas regarding God—but who have not offered to him a worship in harmony with the truth—are liable to the punishments that fall on sinners. (AD 248)
But let us investigate the meaning of this, to be “under sin.” For his words seem to involve all men without exception, whether Jew or Gentile. But another statement of his suggests itself to us, where he says, “But where there is no law, there is no transgression.” Now it is plain that among the Jews there is the law of Moses, whereas among the Gentiles, he asserts, there is the law of nature which convicts the offender by the testimony of his conscience. Well then, where do we look for a man in whom there is no law and who therefore does not seem to be in the transgression of sin? – Commentary on Romans, Book 3, Chapter 2, Section 7 (AD 248)
Methodius
I imagine that He signified by the “sixty queens” [Cant. 6:8, 9] those persons who had pleased God—from the first man who was created, down to Noah. The reason is that these men had no need of commandments and laws for their salvation. For the creation of the world in six days was still recent. . . . These men had great honor, being associated with the angels and often seeing God manifested visibly, and not in a dream. Reflect on the confidence that Seth had towards God—and Abel, Enosh, Enoch, Methuselah, and Noah. These were the first lovers of righteousness. (AD 290)
Lactantius
Since we often see that the worshippers of other gods themselves confess and acknowledge the Supreme God, what pardon can they hope for their impiety? For they do not acknowledge the worship of Him whom man cannot altogether be ignorant of. For in swearing, in expressing a wish, and in giving thanks, they do not name Jupiter, or a number of gods, but only “God.” The truth, of its own accord, entirely breaks forth by the force of nature even from unwilling breasts! (AD 304-313)
If anyone is tossed about on the sea, the wind being furious, it is this God whom he invokes. If anyone is harassed by any violence, he implores His aid. . . . Thus, they never remember God unless it is when they are in trouble. When fear has left them, and the dangers have subsided, then in fact they quickly hasten to the temples of the gods. . . . But to God, whom they called on in their necessity itself, they do not give thanks even in word. (AD 304-313)
Cicero says, . . . “Among men themselves, there is no nation either so uncivilized or so savage that does not know that some conception of Deity should be contemplated, even if they are ignorant of proper conceptions of Him.” (AD 304-313)
Arnobius
Is there any human being who has not entered on the first day of his life with an idea of that Great Ruler? Is there anyone in whom it has not been implanted by nature . . . that God is King and Lord, the Ruler of all things? (AD 305)
Archelaus
From where, then, did righteous Abel and all those succeeding worthies (who are enrolled among the righteous) derive their righteousness? For there was as yet no Law of Moses. . . . Were they not constituted righteous in virtue of their fulfilling the law—“everyone of them showing the work of the law written in their hearts.” . . . For when a man “who does not have the Law does naturally the things contained in the Law, he, not having the Law, is a law unto himself.” – Disputation of Archelaus and Manes (AD 320)