[Romans 10:9-10 NIV] If you declare with your mouth, "Jesus is Lord," and believe in your heart that God raised him from the dead, you will be saved. For it is with your heart that you believe and are justified, and it is with your mouth that you profess your faith and are saved.
These verses mean a lot to me on a personal level. I lean on them with all of my weight for my relationship with God.
Did you realize in Romans 10 Paul is talking about the “righteous which comes by faith” and this whole passage is Paul quoting from Deuteronomy 30? So Deuteronomy 30 is about faith.
Deuteronomy 30:1 (NASB) "So it shall be when all of these things have come upon you, the blessing and the curse which I have set before you, and you call them to mind in all nations where the LORD your God has banished you,
Deuteronomy 30:6 (NASB) "Moreover the LORD your God will circumcise your heart and the heart of your descendants, to love the LORD your God with all your heart and with all your soul, so that you may live.
Deuteronomy 30:11-15 (NASB) 11 "For this commandment which I command you today is not too difficult for you, nor is it out of reach. 12 "It is not in heaven, that you should say, 'Who will go up to heaven for us to get it for us and make us hear it, that we may observe it?' 13 "Nor is it beyond the sea, that you should say, 'Who will cross the sea for us to get it for us and make us hear it, that we may observe it?' 14 "But the word is very near you, in your mouth and in your heart, that you may observe it. 15 "See, I have set before you today life and prosperity, and death and adversity;
Deuteronomy 30:19 (NASB) "I call heaven and earth to witness against you today, that I have set before you life and death, the blessing and the curse. So choose life in order that you may live, you and your descendants,
And we know this is about faith because Paul quotes this passage & tells us it’s about faith:
Romans 10:5-11 (NASB) 5 For Moses writes that the man who practices the righteousness which is based on law shall live by that righteousness. 6 But the righteousness based on faith speaks as follows: "DO NOT SAY IN YOUR HEART, 'WHO WILL ASCEND INTO HEAVEN?' (that is, to bring Christ down), 7 or 'WHO WILL DESCEND INTO THE ABYSS?' (that is, to bring Christ up from the dead)." 8 But what does it say? "THE WORD IS NEAR YOU, IN YOUR MOUTH AND IN YOUR HEART"--that is, the word of faith which we are preaching, 9 that if you confess with your mouth Jesus as Lord, and believe in your heart that God raised Him from the dead, you will be saved; 10 for with the heart a person believes, resulting in righteousness, and with the mouth he confesses, resulting in salvation. 11 For the Scripture says, "WHOEVER BELIEVES IN HIM WILL NOT BE DISAPPOINTED."
The capitalized portions are the quotes from the Old Testament.
So we know that faith is a human choice.
Faith is the proof, because Paul assures us that if we Believe we are justified and if we profess we are saved. Without Belief, there can be no Profession a s FAITH is the gift of God to believe. So Faith is the Proof.
The reason it is faith & not some other trait is because faith is how we qualify as the adopted descendants of Abraham & inherit the righteousness he was given in Genesis 15:5-6 which was promised as an everlasting inheritance to his descendants in Genesis 17:7.
When we have the same faith in the gospel of Jesus Christ that he had (Gal 3:7-9), we become qualified as adopted heirs (Rom 8:15-17, Gal 3:8,29). Faith is the qualifier because this was the pattern of righteousness by grace through faith in the gospel of Christ that God established with his covenant of faith with Abraham.