God's creation is part of his revelation of himself.
Scripture says that everyone has some idea of God. It's undeniable that many non-Christians are seeking God - they may have false ideas about Him but they're seeking Him nonetheless, and NO ONE can seek God except on God's initiative. The fact that they're seeking God, however imperfectly, shows that He is working in their lives.
Romans 1:18-21 says "The wrath of God is indeed being revealed from heaven against every impiety and wickedness of those who suppress the truth by their wickedness. For what can be known about God is evident to them, because God made it evident to them. Ever since the creation of the world, his invisible attributes of eternal power and divinity have been able to be understood and perceived in what he has made. As a result, they have no excuse; for although they knew God they did not accord him glory as God or give him thanks. Instead, they became vain in their reasoning, and their senseless minds were darkened."
So here scripture explicitly says that one can know God by natural revelation, right? Someone who does evil can’t legitimately claim that he never knew about God, because God made sure through creation that everyone knows about him. The passage doesn’t say that they’re wicked because they don’t know God, what it says is that they’re wicked because they know God well enough and they reject him anyway!
A Protestant might say that that level of knowledge is not salvific, that you can’t be saved if that’s the limit of your knowledge of God. But there are two problems with that viewpoint. First, that would mean that people are lost because God requires them to know what they cannot know, and they cannot know it because God didn’t allow them to know it. That would violate God’s perfect justice. Second, it would mean that one can only be saved through the attainment of information which is hidden to all but a select few, which is at the core of the gnostic heresies.
If one has to have heard of Jesus in order to be saved, then never having had the opportunity to hear of him is a really good excuse for never having heard of him. But the bible specifically says that even these people have no excuse for rejecting God, because they did know about him and they rejected him anyway. What gets you into hell is rejecting God. If you don’t know about Jesus then you can’t very well be culpable for rejecting him, because you can only reject what you know about. God holds us accountable only for what we know, and not for what we cannot know.
And so the Church teaches that even these people may be saved (not that they
will be saved, but only that they
may be saved) through the merits of Christ, by means of which we do not know.
I like the way C. S. Lewis said it in Chapter 15 of The Last Battle. In it, Emeth tells of his meeting with Aslan:
Then I fell at his feet and thought, Surely this is the hour of death, for the Lion (who is worthy of all honor) will know that I have served Tash all my days and not him. Nevertheless, it is better to see the Lion and die than to be Tisroc of the world and live and not to have seen him. But the Glorious One bent down his golden head and touched my forehead with his tongue and said, "Son, thou art welcome." But I said, "Alas, Lord, I am no son of thine but the servant of Tash." He answered, "Child, all the service thou hast done to Tash, I account as service done to me." Then by reason of my great desire for wisdom and understanding, I overcame my fear and questioned the Glorious One and said "Lord, is it then true, as the Ape said, that thou and Tash are one"" The Lion growled so that the earth shook (but his wrath was not against me) and said, "It is false. Not because he and I are one, but because we are opposites - I take to me the services which thou hast done to him. For he and I are of such different kinds that no service which is vile can be done to me, and none which is not vile can be done to him. Therefore, if any man swear by Tash and keep his oath for the oath's sake, it is by me that he has truly sworn, though he know it not, and it is I who reward him. And if any man do cruelty in my name, then, though he says the name Aslan, it is Tash whom he serves and by Tash his deed is accepted. Dost thou understand, Child?" I said "Lord, thou knowest how much I understand." But I said also (for the truth constrained me), "Yet I have been seeking Tash all my days." "Beloved," said the Glorious One, "unless thy desire had been for me thou wouldst not have sought so long and so truly. For all find what they truly seek."
Anyone who is saved, is saved through Christ