Revelation refers to the revealing of something that was previously unknown. In the case of theology, revelation refers to the revealing of the knowledge of God’s character and ways.
The Bible presents two types of revelation.
1) General revelation refers to the knowledge of God that is revealed in creation. This is spoken of in Scripture in places like Psalm 19:1-2:
The heavens declare the glory of God, and the sky above proclaims his handiwork. Day to day pours out speech, and night to night reveals knowledge.
Scripture teaches that, because of what is evident in creation, every human being has received enough knowledge about God to be justly condemned before him for their sinful rebellion against his rule. As Paul says in Romans 1:18-20,
For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth. For what can be known about God is plain to them, because God has shown it to them. For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse.
2) Special revelation refers to the knowledge of God that comes to us supernaturally through prophetic words. Today it refers most particularly to the words of prophecy that have been recorded for us in the Bible. Paul speaks of this kind of revelation in 2 Timothy 3:14-15:
But as for you [Timothy], continue in what you have learned and have firmly believed, knowing from whom you learned it and how from childhood you have been acquainted with the sacred writings, which are able to make you wise for salvation through faith in Christ Jesus.
Scripture teaches that, apart from a new, supernatural word from God, every human is consigned to the condemnation they have received through General revelation.
For “everyone who calls on the name of the Lord will be saved.” How then will they call on him in whom they have not believed? And how are they to believe in him of whom they have never heard? And how are they to hear without someone preaching? And how are they to preach unless they are sent? As it is written, “How beautiful are the feet of those who preach the good news!” (Romans 10:13-15)
Despite humanity’s sinful rejection of him in general revelation, God has graciously, mercifully sent another Word, one of mercy and reconciliation through the death of his Son. And all who receive and rely on this revelation will be saved.