Psalm 19:14 says, "May the words of my mouth and the meditations of my heart be pleasing to you, O Lord my God". As a follower of Christ, we need to fill our mind, emotions, and our words with the word of God, so that we resemble Jesus Christ in every way.
According to Trevor Moawad in the interview on the youtube show, Impact Theory, he said "If somebody says aloud, it is the times more powerful than if they think it...when I say things out loud, it is 10X, if it is negative, 40 to 70 times more likely that would happen than I would not say anything."
Pastor Joon Hwang challenges that we need to say out out the Word of God from the Bible, not just to think them, so that we can actually experience what is in the Bible happening to our lives. There is a power in saying the Word of God out loud.