When you speak what God says, it does several things. When you speak the Word out of your mouth, you are planting a seed. Not only that ... but "faith comes by hearing, and hearing by the Word of God!" (Romans 10:17). The more you believe the Word, the more you'll speak it.
In 2 Corinthians 4:13 Paul said: "We, having the same spirit of faith, according as it is written, I believed, and therefore have I spoken; we also believe, and therefore speak."
Paul was quoting Psalm 116:10, which says in part, "I believed, therefore have I spoken." Then he said, "We also believe, and therefore speak." In other words, what you believe, you will speak. But even if you don't believe the Word, if you speak it long enough, you will eventually believe it, and then you'll be bold to speak it. It is God's cycle for producing faith as well as planting seed for harvest.
This is the way that you get the process going. It's in your mouth, then it's in your heart. When it's in your heart in abundance, it will stay in your mouth. For out of the abundance of the heart the mouth speaks. You can usually locate people and tell where they are spiritually by the words they speak. Just hang around them for a few minutes ... and that which is abundantly in their heart always shows up in their mouth.
Sometimes they don't like what's in their mouth. One day a man I know came out with a few of his choice curse words. Then he slapped his hand over his mouth and said, "Oh, I don't talk that way anymore!"
What he meant was that he didn't intend to talk that way around me, but what was in his heart got in his mouth.
Whatever is in your heart will always tell on you ... doubt, fear, or unbelief ... you will talk about it. If you are in faith, you will talk faith.
Mark 4:26 ... Jesus said that the Kingdom of God is "as if a man should cast seed into the ground ......". You need to understand that God is not sowing your seed for you. It's not going to manifest for you just because it's in the Bible and you happened to read it.
When you speak the Word of Promise out of your mouth, it is picked up by the inner ear and planted into the heart.
Reverend Robert W. & Mary C. Butler