The power of words is a topic of study that could last a lifetime..especially in the application.  Understandably, words can heal and soothe or they can wound and hurt. We must realize that our words can be be words of life or words of death.  In learning to speak words of life, our hearts must first be filled with the goodness of God relative to the revealing of His heart in the scriptures and fully declared in the life of Jesus.  Only then can we legitimately speak the true words of life, emanating from the spirit within as we are transformed.
 
It makes total sense that our thoughts are related to our hearts, which forms its substance from the type of thoughts we dwell on and think upon day by day.