Romans 10:8-14
8 But what saith it? The word is nigh thee, even in thy mouth, and in thy heart: that is, the word of faith, which we preach;
9 That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.
10 For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
11 For the scripture saith, Whosoever believeth on him shall not be ashamed.
12 For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him.
13 For whosoever shall call upon the name of the Lord shall be saved.
14 How then shall they call on him in whom they have not believed? and how shall they believe in him of whom they have not heard? and how shall they hear without a preacher?
The Grace New Testament Commentary - Romans 10:9-10
10:9 The response of the mouth should be a confession directly addressing Jesus with the designation "Lord." This confession is made in prayer (vv 12-13). This is an appeal to His Lordship for the needed deliverance from divine wrath.
The direct appeal to Lord Jesus necessitates that the one who makes the appeal should believe that Jesus is alive to hear it. Thus, the attitude of the heart is crucial. When one calls on Jesus with his mouth in order to be delivered, he therefore must have faith in his heart that God has raised Him from the dead. When these two conditions obtain, the individual Jew who calls on Him will be delivered from God's temporal wrath.
10:10 What happens in the heart, though vital, is not enough for deliverance. The heart is where it all begins. One gets righteousness by the believing response of the heart. Jesus is the object of that faith.
But in the same way, He is also the object of our confession: "but with the mouth He is confessed for deliverance". The Jerusalem Bible captures the actual sense almost perfectly: "By believing from the heart you are made righteous; by confessing with your lips you are saved." While the Jew is granted righteousness on the basis of faith in his heart, God will not grant him deliverance on the basis of that faith alone. He must also confess with his mouth.