Although natural revelation and special revelation are both from God, the latter is like a pair of spectacles (so says Calvin) that helps us to understand everything else. Natural revelation was sufficient before the Fall. And if Adam and Eve had not fallen into sin, it still would be sufficient. The Bible only came about because of the Fall. We can’t see properly unless we put on the spectacles.
The above quote came from Lane Keister in a post concerning the reinstatement of theology as the "queen of the sciences." The reason I bring up this section of his post is because I think it includes one of the continuing difficulties that some Reformed folks have with understanding the nature of man in the Garden of Eden prior to the Fall.
If Natural Revelation (NR) is defined as what God has revealed in Creation, apart from any Divine Word, then it is not true that it was sufficient before the Fall. Why not, you ask? Well, the most important reason is that NR does not provide commandments for men to follow, which means that NR could not provide Adam and Eve with the standards necessary for pleasing God in the Garden. Only God's Law-Word could give Adam and Eve the stipulations or requirements for maintaining their holy and obedient status. This is, in fact, what God provided by commanding Adam and Eve to be fruitful, multiply, and fill the earth; and to subdue it and care for it. It is also what God provided when He prohibited Adam and Eve from partaking of the fruit of the tree in the midst of the garden, lest in eating they transgress and die.
But even if Lane were to qualify his claim so that the pronouncement of Law becomes one exception to the sufficiency of NR in the Garden, he would still suffer from a deficiency. For not only is God's Law-Word required in the Garden, so is His declaration of truth and of blessing. To assume that Adam could intuit from Creation alone all that he was intended to do is to assume that he did not require communion with God in terms of truth and blessing. There is some precedent for thinking that Adam was well equipped to manage Creation on his own. For instance, when God brings the animals to man, the text indicates that Adam named them, but it does not imply that Adam sought out God for knowledge of these names. However, we may wonder how Adam would have been assured that his pronouncements were good and right without God's blessing them and pronouncing them acceptable in His sight. What honorable son does not bring his work before his father for the father's approval? Moreover, how would Adam have known he lacked a counterpart unless God had delivered unto him the animals and given him the task of naming them? God's direction is as much a requirement in the Garden prior to the Fall as it is after the Fall.
As much of a "superman" as Adam may have been, it is obvious that Adam's righteousness and abilities to honor God did not exceed those of Christ, and yet Christ explicitly says that everything He does, He does because it is what His Father has told Him to say or do. In other words, the Divine Word is necessary for the proper functioning of man. Natural Revelation is not sufficient whether prior to the Fall, or after the Fall, to provide man with the proper knowledge he requires to satisfy the Father. And why should it, since the whole purpose of man is to be in communion with God, which certainly implies verbal communication.
So while it is good to affirm with Lane the need for Biblical presuppositions to govern scientific endeavors, it does not require us to accept that Natural Revelation can provide man with the sort of positive knowledge of God that Lane seems to believe it does. Natural Revelation is able to confirm all that Special Revelation provides, and certainly Natural Revelation provides all that is necessary to hold men accountable for their offenses against God. But Natural Revelation is not sufficient for providing man with the knowledge of God that he requires to commune properly with God, in any state of man--whether pre-Fall state, post-Fall state, Redeemed state, or Glorified state.