First, for the sake of clarity it is helpful to distinguish between God’s revelation of Himself through creation, and natural theology, which is our interpretation of that revelation. Most of us wish to interpret the physical world around us—stars and trees and roses—as being sufficient to lead a sinner to God. We worry about those who never heard the gospel.
Second, however, we have to acknowledge that after the Fall, each of us naturally possesses a lust for idols and a flawed natural theology. In much of the ancient world, and in Africa today, it is widely believed that God made earth and sky, fire and water. That, and not much else, is their “natural theology.” That theology is insufficient to lead people to repentance (see Acts 17:30–31).
Finally, the subject in Romans 1:18–32 is only indirectly concerned with the nature of God’s revelation of Himself in creation, and man’s interpretation of that revelation commonly called natural theology. Instead, the passage deals with the wrath of God in the face of human corruption. It does not say whether a grasp of natural theology leads to salvation. It says, or implies, only that those who have no other source of information about God will be judged according to their response to what they have. Judgment, not salvation is the topic here.