God's word in your mouth is your salvation. His word in your mouth and spoken out properly will produce your salvation. The word says the word of God is powerful(Hebrews 4:12), but for it to be powerful on your behalf it has to come out of your mouth. Romans 1:16 says, For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to everyone that believeth; to the Jew first, and also to the Greek. Notice, it's the power of God unto salvation. That word salvation is translated heal, preserve, save, make well, deliver, rescue. So, the word of God is the power of God unto all of those things, but to him that believeth. Well, according to 2Corinthians 4:13 when you believe you speak. That agrees with Romans 10:10 with your heart you believe and with the mouth you speak. And that combination brings salvation into your life.
That's why Paul says in Romans 10:6-8, you don't have to call Jesus back, but the word is nigh you even in your mouth and in your heart. Notice, it has to be in both places. A lot of people have no problem believing the word has to be in your heart, but they have a problem believing that it has to be in your mouth. But, the Bible has a lot to say about the word being in your mouth and what it will do. Like Proverbs 12:6, the mouth of the upright will deliver them. And the 18th verse of that same chapter says, but the tongue of the wise is health(healing). Proverbs has a lot to say about the words of your mouth like Proverbs 14:3, the lips of the wise shall preserve them. Now we know when the Bible speaks of the mouth, lips, or tongue it is referring to your words. And what better words are there to use than God's words. Because it is He that creates the fruit of your lips (Isaiah 57:19).