“That on which our opponents insist the most, and with the greatest show of argument, is the law and light of nature. This is their professed rule on almost all occasions, and its praises they are continually sounding. I have no desire to depreciate the light of nature, or to disparage its value as a rule. On the contrary, I consider it as occupying an important place in the Divine government. Whatever may be said of the light possessed by the heathen, as being derived from revelation, I feel no difficulty in acknowledging that the grand law which they are under is that of nature. Revelation itself appears to me so to represent it; holding it up as the rule by which they shall be judged, and declaring its dictates to be so clear as to leave them without excuse. Nature and Scripture appear to me to be as much in harmony as Moses and Christ; both are celebrated in the same Psalm.

By the light of nature, however, I do not mean those ideas which heathens have actually entertained, many of which have been darkness, but those which were presented to them by the works of creation, and which they might have possessed, had they been desirous of retaining God in their knowledge. And by the dictates of nature, with regard to right and wrong, I understand those things which appear, to the mind of a person sincerely disposed to understand and practise his duty, to be natural, fit, or reasonable. There is, doubtless, an eternal difference between right and wrong; and this difference, in a vast variety of instances, is manifest to every man who sincerely and impartially considers it. So manifest have the power and Godhead of the Creator been rendered, in every age, that no person of an upright disposition could, through mere mistake, fall into idolatry or impiety; and every one who has continued in these abominations is without excuse. The desire also which every human being feels of having justice done to him from all other persons must render it sufficiently manifest, to his judgment, that he ought to do the same to them; and, wherein he acts otherwise, his conscience, unless it be seared as with a hot iron, must accuse him.

But does it follow from hence that revelation is unnecessary? Certainly not. It is one thing for nature to afford so much light in matters of right and wrong, as to leave the sinner without excuse; and another to afford han any well-grounded hope of forgiveness, or to answer his difficulties concerning the account which something within him says he must hereafter give of his present conduct.

Further, It is one thing to leave sinners without excuse in sin, and another thing to recover them from it. That the light of nature is insufficient for the latter, is demonstrated by melancholy fact. Instead of returning to God and virtue, those nations which have possessed the highest degrees of it have gone further and further into immorality. There is not a single example of a people, of their own accord, returning to the acknowledgment of the true God, or extricating themselves from the most irrational species of idolatry, or desisting from the most odious kinds of vice. Those nations where science diffused a more than ordinary lustre were as superstitious and as wicked as the most barbarous, and in many instances exceeded them.”

Excerpt From “The Gospel Its Own Witness”, 1799

Fuller, Andrew,  The Works of Andrew Fuller. Edinburgh: Banner of Truth Trust, 2007.