When you curse, you tear down, speak negatively and critically. When you bless you speak pleasing, pleasant and profitable words. If you speak curse, curse shall come. If you speak blessing, blessing shall come. God has decreed that words shall play a dominate role in shaping the character and destiny of human beings.
Words are the most powerful, potent force on the face of the earth.
If that which comes out of your mouth is a delight to the Lord, then He brings into performance that which you speak. If the Lord wants the mountain moved, He'll tell you to speak and it will move at your word. God spoke and the world came into existence. Things that were nothing sprung up because God spoke them into existence. The mouth of the righteous is a well of life.