Do you want to know how I know that the Christian religion is the correct religion? Because even the staunchest atheist or universalist or anti-Christian will slam his hand with a hammer and shout out "Jesus!" The excited non-believer will belt, "Oh My God!" Why would these words be on the tips of their tongues, especially with a culture that hates God so?
It's because God has placed knowledge of himself in everyone's hearts. We need the specific revelation of the Bible, but natural revelation alone does give us a knowledge of reality. We may not be able to put our fingers on all the details of reality, but God has placed that eternity in our hearts, so that when missionaries visit unreached people groups, the missionaries are not really introducing the gospel to the group, but reaffirming what these groups have had hints of and have been pondering in their culture and folklore for years, even centuries before.
Listen to Paul:
"The word is near you, on your lips and in your heart" (that is, the word of faith that we proclaim); because if you confess with your lips that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved. For one believes with the heart and so is justified, and one confesses with the mouth and so is saved. The scripture says, "No one who believes in him will be put to shame." For there is no distinction between Jew and Greek; the same Lord is Lord of all and is generous to all who call on him. For, "Everyone who calls on the name of the Lord shall be saved." (Romans 10:8b-13)
To read the last sentence, one would think that taking the Lord's name in vain is preferred. However, we know that there is a commandment, the third, against that. What we are in danger of doing is either the extreme of taking the Lord's name in vain, like an unbeliever, and the extreme of NEVER using the name of the Lord for fear of breaking the commandment, like a Pharisee. We know quite a bit of people in both categories, don't we?
Reading the sentence in context we learn that confessing Jesus as Lord is only half of the equation. We must believe also, with all our heart. But what do we believe? Do we need to believe complicated doctrines about him? No. Paul says right here that we need to believe that God raised him from the dead. Is that all? Yes, it sounds like so. All other faith in Christ will come following after that one belief.
Let's look at this single belief. Is it hard to believe this? Not really. We may have trouble concentrating on believing in an invisible God who doesn't seem to be there or listening. We kneel to pray and we are wondering whether God is really there. Answered prayers elate us temporarily, but then we lapse into unbelief again. The world laughs at our faith, telling us that we need PROOF.
Well, here's the proof. Paul says we have believe with all our heart this one detail about reality, and everything else will follow. What is the detail? That God raised Jesus Christ from the dead. Is that all? Yes! And all that we need to believe is based in historical fact. Did Jesus live? Yes. We have documentation outside the Bible. Only recently have people tried to write the gospels off as complete myth, but all through history, no one denied that Jesus existed. Did Jesus die? Yes. Was he entombed? Yes, we have documents outside of the Bible that testify to that. Did he come back from the dead? The disciples say so. Are they trustworthy? We think so. However, in the extra-Biblical documentation, the Roman officials attempt to explain why the tomb is empty. Never do they DENY that the tomb is empty. They only provide excuses for it being empty. The tomb was empty: that single historical fact catapults our belief into the realm it needs to be. When we believe in the historical fact of the empty tomb, we can then believe that Jesus was raised from the dead. Then we can believe that God the father raised the Son from the dead.
Do we believe this with all our heart? When we believe with all our heart, we are, as Paul puts it, justified. The NASB translation says "righteous," telling the difference between right and wrong. With the confession from our lips, we are saved. Can someone be saved without the righteousness? No. It's a four step progression: belief, righteousness, confession, salvation. Can someone believe and still not be saved because he or she has not confessed the name of the Lord with his or her lips? Yes, it is possible, but God draws that confession out of us. Even if the Pharisees of the church are piling rule upon rule upon us to not confess that name under any circumstances, God draws it out of us. So, although it is possible to have true faith and not be saved, God will not be thwarted in that way, and he brings us to salvation.
Believe with your hearts in the historical resurrection of Jesus. Believe that the Father raised the Son from the dead. He will count it to you as righteousness. Confess the name of the Lord with your lips All who call on the name of the Lord, believing with all their hearts in the historicity of the resurrection, will be saved.