For Moses writes about the righteousness that is based on the law, that the person who does the commandments shall live by them. But the righteousness based on faith says, "Do not say in your heart, 'Who will ascend into heaven?'" (that is, to bring Christ down) or "'Who will descend into the abyss?'" (that is, to bring Christ up from the dead). But what does it say? "The word is near you, in your mouth and in your heart" (that is, the word of faith that we proclaim); because, if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved. For with the heart one believes and is justified, and with the mouth one confesses and is saved. For the Scripture says, "Everyone who believes in him will not be put to shame." For there is no distinction between Jew and Greek; for the same Lord is Lord of all, bestowing his riches on all who call on him. For "everyone who calls on the name of the Lord will be saved."
"With that confession Paul links believing in the heart. The reference to the heart points to the inwardness of faith; Paul is not referring to a superficial confession, accompanied by no more than a token faith. He is referring to a faith that takes hold of the whole of the inner man...It means that faith has content; Paul is not advocating a fideism in which all that matters is to believe. To Paul it matters that we believe, but it also matters what we believe. Here he speaks of believing that God raised him from the dead. The resurrection is of critical importance. It is at the cross that God did his saving work, but Paul does not believe in a dead martyr but in a living Savior." -Leon Morris (Commentary on Romans)Grace and Peace,
Stephen