9 If you openly declare that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved. 10 For it is by believing in your heart that you are made right with God, and it is by openly declaring your faith that you are saved. 11 As the Scriptures tell us, “Anyone who trusts in him will never be disgraced.” 12 Jew and Gentile are the same in this respect. They have the same Lord, who gives generously to all who call on him. 13 For “Everyone who calls on the name of the Lord will be saved.”
Paul makes it clear throughout the whole book of Romans how we are saved, or made right with God. It is by faith, trusting in the promises God made with us through Christ. What the Law could not do for us, Jesus did by dying for us on the cross. So when Paul says today, "If you openly declare that Jesus is Lord and believe in your heart that God raised him from the dead you will be saved", he is not advocating you have to do anything to be saved.
He reiterates that if you "believe in your heart" you will be saved. To "believe" means to have faith. Faith comes when we hear the saving Word of God, and believe it in the power of the Holy Spirit. As a result of this life saving faith, we confess what we believe. Not to obtain faith or God's acceptance, but because we have it. Faith is a gift of God which we receive and then express through our lips. Because faith changes us, as we become a new creation in Christ, our lips express what we have experienced by God's grace.
It is also powerful when we publicly declare our faith. It doesn't make us any more right with God, but it externalizes something that is internal. It verifies to the outside world soemthing that has happened to and in us. It might be safe to say that anyone who has experienced saving faith through Jesus Christ would have a really hard time keeping it to themselves. Though not a perfect analogy, it would be like if someone won the lottery and didn't tell anybody about it.
When we truly experience God's saving and amazing grace, we cannot keep it inside. This why the greatest source of evangelism is Christians themselves when they realize God's grace. You can argue against propositions and arguments about the Christian faith, but you can't argue against a changed life. It was the eyewitness testimony of the early apostles that grew the early church. As they witnessed to what Jesus had done for them and all people, others came to believe and experience God's grace. Then they shared with others.
It is a powerful experience to give public witness to your faith. When our lips confess what is true in our heart.But let's rememeber how we are saved. We are save when we trust in Jesus Christ as our Lord and Savior. And that to is a gift given to us lest we should boast.